diff --git a/src/LageBuch.App.Android/MainActivity.cs b/src/LageBuch.App.Android/MainActivity.cs
index 21d06b6..0aee49d 100644
--- a/src/LageBuch.App.Android/MainActivity.cs
+++ b/src/LageBuch.App.Android/MainActivity.cs
@@ -65,6 +65,7 @@ protected override AppBuilder CustomizeAppBuilder(AppBuilder builder)
             new NoopIncidentHostController(),
             new LageBuch.App.Shared.Services.AvaloniaUiDispatcher(),
             typeof(MainActivity).Assembly.GetName().Version?.ToString() ?? "0.0.0",
+            AndroidAppPaths.RegionsDir(this),
             lastSaveFolder: null,
             attachmentCacheRoot: AndroidAppPaths.AttachmentCacheDir(this));
         return base.CustomizeAppBuilder(builder).WithInterFont();
diff --git a/src/LageBuch.App.Android/Services/AndroidAppPaths.cs b/src/LageBuch.App.Android/Services/AndroidAppPaths.cs
index 62deec0..d053fb9 100644
--- a/src/LageBuch.App.Android/Services/AndroidAppPaths.cs
+++ b/src/LageBuch.App.Android/Services/AndroidAppPaths.cs
@@ -27,4 +27,7 @@ public static string RecentFilesJsonPath(Context context) =>
 
     public static string AttachmentCacheDir(Context context) =>
         System.IO.Path.Combine(CacheDir(context), "attachment-cache");
+
+    public static string RegionsDir(Context context) =>
+        System.IO.Path.Combine(context.FilesDir!.AbsolutePath, "regions");
 }
diff --git a/src/LageBuch.App.Shared/CompositionRoot.cs b/src/LageBuch.App.Shared/CompositionRoot.cs
index 9d7bd52..d8a09e9 100644
--- a/src/LageBuch.App.Shared/CompositionRoot.cs
+++ b/src/LageBuch.App.Shared/CompositionRoot.cs
@@ -14,6 +14,13 @@ namespace LageBuch.App.Shared;
 /// </summary>
 public static class CompositionRoot
 {
+    /// <summary>
+    /// Raw-served manifest of published Wasserförderung region packs (#150 follow-up) — see
+    /// tools/build-region-pack/README.md for how a pack is built and published here.
+    /// </summary>
+    public const string RegionPackManifestUrl =
+        "https://raw.githubusercontent.com/CodeForFire/lagebuch-regions/main/regions.json";
+
     public static MainWindowViewModel CreateMainWindowViewModel(
         IIncidentStore store,
         IMasterDataProvider masterData,
@@ -26,11 +33,15 @@ public static MainWindowViewModel CreateMainWindowViewModel(
         IIncidentHostController hostController,
         IUiDispatcher uiDispatcher,
         string appVersion,
+        string regionsDir,
         ILastSaveFolderStore? lastSaveFolder = null,
         string? attachmentCacheRoot = null)
     {
         var home = new HomeViewModel(store, masterData, recent, dialogs, clock, ticker, alarm, hostController, appVersion, uiDispatcher, lastSaveFolder, attachmentCacheRoot, new RouteOverviewRenderer());
-        var editor = new MasterDataEditorViewModel(masterData, dialogs, masterDataFileService);
+        var httpClient = new HttpClient();
+        var regionCatalog = new RegionPackCatalogService(httpClient, RegionPackManifestUrl);
+        var regionInstaller = new RegionPackInstaller(httpClient, regionsDir);
+        var editor = new MasterDataEditorViewModel(masterData, dialogs, masterDataFileService, regionCatalog, regionInstaller);
         return new MainWindowViewModel(home, editor, dialogs, appVersion);
     }
 }
diff --git a/src/LageBuch.App.Shared/Views/MasterDataEditorView.axaml b/src/LageBuch.App.Shared/Views/MasterDataEditorView.axaml
index 2561551..8bdea8f 100644
--- a/src/LageBuch.App.Shared/Views/MasterDataEditorView.axaml
+++ b/src/LageBuch.App.Shared/Views/MasterDataEditorView.axaml
@@ -2,6 +2,7 @@
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:vm="clr-namespace:LageBuch.AppLogic.ViewModels;assembly=LageBuch.AppLogic"
              xmlns:md="clr-namespace:LageBuch.Persistence.MasterData;assembly=LageBuch.Persistence"
+             xmlns:services="clr-namespace:LageBuch.AppLogic.Services;assembly=LageBuch.AppLogic"
              x:Class="LageBuch.App.Shared.Views.MasterDataEditorView"
              x:DataType="vm:MasterDataEditorViewModel">
   <Panel>
@@ -108,18 +109,63 @@
                 </ScrollViewer>
               </DataTemplate>
 
-              <!-- Wasserförderung region of operation (#150 phase 2) -->
+              <!-- Wasserförderung region of operation (#150 phase 2 + region-pack follow-up):
+                   pick a published pack from the catalog and download it; manual folder entry
+                   stays available under "Erweitert" for a self-built or hand-placed pack. -->
               <DataTemplate x:DataType="vm:EinsatzgebietSection">
-                <StackPanel Spacing="12" MaxWidth="440" HorizontalAlignment="Left">
-                  <StackPanel Spacing="4">
-                    <TextBlock Text="NAME" Classes="overline" FontSize="10" />
-                    <TextBox Text="{Binding Name}" PlaceholderText="z. B. Landkreis Fürstenfeldbruck" />
-                  </StackPanel>
-                  <StackPanel Spacing="4">
-                    <TextBlock Text="ORDNER (region.mbtiles + region.dem)" Classes="overline" FontSize="10" />
-                    <TextBox Text="{Binding FolderPath}" PlaceholderText="z. B. /var/lib/lagebuch/regions/ffb" />
+                <ScrollViewer>
+                  <StackPanel Spacing="12" MaxWidth="480" HorizontalAlignment="Left">
+                    <StackPanel Spacing="4">
+                      <TextBlock Text="KARTENPAKET" Classes="overline" FontSize="10" />
+                      <Grid ColumnDefinitions="*,Auto" ColumnSpacing="8">
+                        <ComboBox x:Name="RegionComboBox" Grid.Column="0" HorizontalAlignment="Stretch"
+                                  ItemsSource="{Binding AvailableRegions}"
+                                  SelectedItem="{Binding SelectedRegion}"
+                                  PlaceholderText="Region auswählen…">
+                          <ComboBox.ItemTemplate>
+                            <DataTemplate x:DataType="services:RegionPackInfo">
+                              <TextBlock Text="{Binding Name}" />
+                            </DataTemplate>
+                          </ComboBox.ItemTemplate>
+                        </ComboBox>
+                        <Button x:Name="DownloadButton" Grid.Column="1" Content="HERUNTERLADEN"
+                                Command="{Binding DownloadSelectedRegionCommand}" />
+                      </Grid>
+                    </StackPanel>
+
+                    <Border x:Name="CatalogStatusBanner"
+                            IsVisible="{Binding CatalogStatus, Converter={x:Static ObjectConverters.IsNotNull}}"
+                            Background="#241608" BorderBrush="{StaticResource AmberBrush}" BorderThickness="1"
+                            CornerRadius="{StaticResource RadiusSm}" Padding="8,6">
+                      <TextBlock Text="{Binding CatalogStatus}" FontSize="12"
+                                 Foreground="{StaticResource AmberBrush}" TextWrapping="Wrap" />
+                    </Border>
+
+                    <ProgressBar x:Name="DownloadProgressBar" Minimum="0" Maximum="1"
+                                 Value="{Binding DownloadProgress}" Height="4" />
+
+                    <TextBlock x:Name="AttributionText" Text="{Binding SelectedRegion.Attribution}"
+                               IsVisible="{Binding SelectedRegion, Converter={x:Static ObjectConverters.IsNotNull}}"
+                               Classes="secondary" FontSize="11" TextWrapping="Wrap" />
+
+                    <TextBlock x:Name="KartendatenStatusText" Text="{Binding KartendatenStatus}"
+                               IsVisible="{Binding KartendatenStatus, Converter={x:Static ObjectConverters.IsNotNull}}"
+                               FontSize="12" TextWrapping="Wrap" />
+
+                    <Expander Header="Erweitert (manueller Ordnerpfad)">
+                      <StackPanel Spacing="12" Margin="0,12,0,0">
+                        <StackPanel Spacing="4">
+                          <TextBlock Text="NAME" Classes="overline" FontSize="10" />
+                          <TextBox Text="{Binding Name}" PlaceholderText="z. B. Landkreis Fürstenfeldbruck" />
+                        </StackPanel>
+                        <StackPanel Spacing="4">
+                          <TextBlock Text="ORDNER (region.mbtiles + region.dem)" Classes="overline" FontSize="10" />
+                          <TextBox Text="{Binding FolderPath}" PlaceholderText="z. B. /var/lib/lagebuch/regions/ffb" />
+                        </StackPanel>
+                      </StackPanel>
+                    </Expander>
                   </StackPanel>
-                </StackPanel>
+                </ScrollViewer>
               </DataTemplate>
 
               <!-- String-list / checklist editor -->
diff --git a/src/LageBuch.App/AppPaths.cs b/src/LageBuch.App/AppPaths.cs
index 48937db..4d44bd7 100644
--- a/src/LageBuch.App/AppPaths.cs
+++ b/src/LageBuch.App/AppPaths.cs
@@ -13,6 +13,9 @@ public static class AppPaths
 
     public static string AttachmentCacheDir => Path.Combine(AppDataDir, "attachment-cache");
 
+    /// <summary>Where downloaded Wasserförderung region packs (#150 follow-up) get extracted, one subfolder per slug.</summary>
+    public static string RegionsDir => Path.Combine(AppDataDir, "regions");
+
     public static string GetAppDataDir(string baseDir)
     {
         var dir = Path.Combine(baseDir, "Lagebuch");
diff --git a/src/LageBuch.App/Program.cs b/src/LageBuch.App/Program.cs
index f36d325..2fa7e10 100644
--- a/src/LageBuch.App/Program.cs
+++ b/src/LageBuch.App/Program.cs
@@ -37,6 +37,7 @@ private static MainWindowViewModel CreateMainViewModel()
             new IncidentHostController(clock, version, uiDispatcher),
             uiDispatcher,
             version,
+            AppPaths.RegionsDir,
             new JsonLastSaveFolderStore(AppPaths.LastSaveFolderJsonPath),
             AppPaths.AttachmentCacheDir);
     }
diff --git a/src/LageBuch.AppLogic/Services/IRegionPackCatalogService.cs b/src/LageBuch.AppLogic/Services/IRegionPackCatalogService.cs
new file mode 100644
index 0000000..58286bc
--- /dev/null
+++ b/src/LageBuch.AppLogic/Services/IRegionPackCatalogService.cs
@@ -0,0 +1,28 @@
+namespace LageBuch.AppLogic.Services;
+
+/// <summary>
+/// Lists the region packs (map tiles + elevation) publicly available for download (#150 follow-up)
+/// — the map-side counterpart to Stammdaten's Einsatzgebiet, which used to require hand-preparing
+/// region.mbtiles/region.dem with no guidance at all.
+/// </summary>
+public interface IRegionPackCatalogService
+{
+    /// <summary>
+    /// Never throws — a Stammdaten editor must stay usable offline, so a fetch/parse failure
+    /// yields an empty list rather than propagating an exception.
+    /// </summary>
+    Task<IReadOnlyList<RegionPackInfo>> GetAvailableRegionsAsync(CancellationToken ct = default);
+}
+
+/// <summary>One published, downloadable region pack.</summary>
+public sealed record RegionPackInfo(
+    string Name,
+    string Slug,
+    string DownloadUrl,
+    long SizeBytes,
+    double MinLat,
+    double MinLon,
+    double MaxLat,
+    double MaxLon,
+    string BuiltAt,
+    string Attribution);
diff --git a/src/LageBuch.AppLogic/Services/IRegionPackInstaller.cs b/src/LageBuch.AppLogic/Services/IRegionPackInstaller.cs
new file mode 100644
index 0000000..1b3e45a
--- /dev/null
+++ b/src/LageBuch.AppLogic/Services/IRegionPackInstaller.cs
@@ -0,0 +1,8 @@
+namespace LageBuch.AppLogic.Services;
+
+/// <summary>Downloads and unpacks a region pack (#150 follow-up) into a local folder.</summary>
+public interface IRegionPackInstaller
+{
+    /// <summary>Returns the folder the pack was extracted into (ready to use as Einsatzgebiet.FolderPath).</summary>
+    Task<string> DownloadAndInstallAsync(RegionPackInfo pack, IProgress<double>? progress, CancellationToken ct = default);
+}
diff --git a/src/LageBuch.AppLogic/Services/RegionPackCatalogJson.cs b/src/LageBuch.AppLogic/Services/RegionPackCatalogJson.cs
new file mode 100644
index 0000000..08df716
--- /dev/null
+++ b/src/LageBuch.AppLogic/Services/RegionPackCatalogJson.cs
@@ -0,0 +1,85 @@
+using System.Text.Json;
+using System.Text.RegularExpressions;
+
+namespace LageBuch.AppLogic.Services;
+
+/// <summary>
+/// Reads the region-pack manifest format (#150 follow-up) — a flat JSON array, each entry
+/// describing one downloadable pack. Defensive like <c>MasterDataJson</c>: malformed input, or an
+/// entry missing a required field, is skipped rather than thrown — the manifest is fetched from a
+/// third-party-controlled URL, so a partially bad response must degrade gracefully, not crash
+/// Stammdaten.
+/// </summary>
+public static class RegionPackCatalogJson
+{
+    // RegionPackInstaller joins this straight onto a base directory (<regionsBaseDir>/<slug>) —
+    // reject anything that could escape that directory (path separators, "..", empty) here rather
+    // than trusting the installer alone to catch it.
+    private static readonly Regex SafeSlug = new("^[a-z0-9][a-z0-9_-]{0,63}$", RegexOptions.Compiled);
+
+    public static IReadOnlyList<RegionPackInfo> Parse(string json)
+    {
+        try
+        {
+            using var doc = JsonDocument.Parse(json);
+            if (doc.RootElement.ValueKind != JsonValueKind.Array)
+                return Array.Empty<RegionPackInfo>();
+
+            var result = new List<RegionPackInfo>();
+            foreach (var entry in doc.RootElement.EnumerateArray())
+            {
+                if (TryParseEntry(entry, out var region))
+                    result.Add(region);
+            }
+            return result;
+        }
+        catch (JsonException)
+        {
+            return Array.Empty<RegionPackInfo>();
+        }
+    }
+
+    private static bool TryParseEntry(JsonElement entry, out RegionPackInfo region)
+    {
+        region = null!;
+        if (entry.ValueKind != JsonValueKind.Object)
+            return false;
+
+        if (!TryGetString(entry, "name", out var name) ||
+            !TryGetString(entry, "slug", out var slug) || !SafeSlug.IsMatch(slug) ||
+            !TryGetString(entry, "downloadUrl", out var downloadUrl) ||
+            !TryGetString(entry, "builtAt", out var builtAt) ||
+            !TryGetString(entry, "attribution", out var attribution) ||
+            !entry.TryGetProperty("sizeBytes", out var sizeBytesEl) || sizeBytesEl.ValueKind != JsonValueKind.Number ||
+            !entry.TryGetProperty("boundingBox", out var bbox) || bbox.ValueKind != JsonValueKind.Object ||
+            !TryGetNumber(bbox, "minLat", out var minLat) ||
+            !TryGetNumber(bbox, "minLon", out var minLon) ||
+            !TryGetNumber(bbox, "maxLat", out var maxLat) ||
+            !TryGetNumber(bbox, "maxLon", out var maxLon))
+        {
+            return false;
+        }
+
+        region = new RegionPackInfo(name, slug, downloadUrl, sizeBytesEl.GetInt64(),
+            minLat, minLon, maxLat, maxLon, builtAt, attribution);
+        return true;
+    }
+
+    private static bool TryGetString(JsonElement e, string prop, out string value)
+    {
+        value = string.Empty;
+        if (!e.TryGetProperty(prop, out var v) || v.ValueKind != JsonValueKind.String)
+            return false;
+        value = v.GetString()!;
+        return true;
+    }
+
+    private static bool TryGetNumber(JsonElement e, string prop, out double value)
+    {
+        value = 0;
+        if (!e.TryGetProperty(prop, out var v) || v.ValueKind != JsonValueKind.Number)
+            return false;
+        value = v.GetDouble();
+        return true;
+    }
+}
diff --git a/src/LageBuch.AppLogic/Services/RegionPackCatalogService.cs b/src/LageBuch.AppLogic/Services/RegionPackCatalogService.cs
new file mode 100644
index 0000000..dd6e0bb
--- /dev/null
+++ b/src/LageBuch.AppLogic/Services/RegionPackCatalogService.cs
@@ -0,0 +1,23 @@
+namespace LageBuch.AppLogic.Services;
+
+/// <summary>
+/// Fetches the region-pack manifest over HTTP (#150 follow-up). The one place this offline-first
+/// app makes an unprompted network call — but only when the operator opens the Einsatzgebiet
+/// section, and it degrades to an empty list rather than surfacing any error, so Stammdaten stays
+/// fully usable without a connection.
+/// </summary>
+public sealed class RegionPackCatalogService(HttpClient httpClient, string manifestUrl) : IRegionPackCatalogService
+{
+    public async Task<IReadOnlyList<RegionPackInfo>> GetAvailableRegionsAsync(CancellationToken ct = default)
+    {
+        try
+        {
+            var json = await httpClient.GetStringAsync(manifestUrl, ct);
+            return RegionPackCatalogJson.Parse(json);
+        }
+        catch (HttpRequestException)
+        {
+            return Array.Empty<RegionPackInfo>();
+        }
+    }
+}
diff --git a/src/LageBuch.AppLogic/Services/RegionPackInstaller.cs b/src/LageBuch.AppLogic/Services/RegionPackInstaller.cs
new file mode 100644
index 0000000..d8bd319
--- /dev/null
+++ b/src/LageBuch.AppLogic/Services/RegionPackInstaller.cs
@@ -0,0 +1,63 @@
+using System.IO.Compression;
+
+namespace LageBuch.AppLogic.Services;
+
+/// <summary>
+/// Downloads a region pack's zip (region.mbtiles + region.dem) and extracts it into
+/// <c>&lt;regionsBaseDir&gt;/&lt;slug&gt;</c> (#150 follow-up). A re-install of the same slug replaces the
+/// folder outright, so a pack update never leaves stale files from a previous version behind.
+/// </summary>
+public sealed class RegionPackInstaller(HttpClient httpClient, string regionsBaseDir) : IRegionPackInstaller
+{
+    // Downloading is the slow part; reserve a small tail of the progress range for extraction so
+    // the caller sees forward motion continue past "download done" instead of jumping straight to 1.0.
+    private const double DownloadProgressShare = 0.9;
+
+    public async Task<string> DownloadAndInstallAsync(RegionPackInfo pack, IProgress<double>? progress, CancellationToken ct = default)
+    {
+        progress?.Report(0.0);
+
+        var zipBytes = await DownloadAsync(pack.DownloadUrl, progress, ct);
+
+        // Defense in depth: RegionPackCatalogJson already rejects unsafe slugs when parsing the
+        // manifest, but a slug ending up here from anywhere else must not be able to escape
+        // regionsBaseDir either.
+        var baseFull = Path.GetFullPath(regionsBaseDir) + Path.DirectorySeparatorChar;
+        var folder = Path.GetFullPath(Path.Combine(regionsBaseDir, pack.Slug));
+        if (!folder.StartsWith(baseFull, StringComparison.Ordinal))
+            throw new InvalidOperationException($"Region slug '{pack.Slug}' escapes the regions directory.");
+
+        if (Directory.Exists(folder))
+            Directory.Delete(folder, recursive: true);
+        Directory.CreateDirectory(folder);
+
+        using (var zip = new ZipArchive(new MemoryStream(zipBytes), ZipArchiveMode.Read))
+            zip.ExtractToDirectory(folder);
+
+        progress?.Report(1.0);
+        return folder;
+    }
+
+    private async Task<byte[]> DownloadAsync(string url, IProgress<double>? progress, CancellationToken ct)
+    {
+        using var response = await httpClient.GetAsync(url, HttpCompletionOption.ResponseHeadersRead, ct);
+        response.EnsureSuccessStatusCode();
+
+        var totalBytes = response.Content.Headers.ContentLength;
+        await using var source = await response.Content.ReadAsStreamAsync(ct);
+        using var buffer = new MemoryStream();
+
+        var chunk = new byte[81920];
+        long readSoFar = 0;
+        int read;
+        while ((read = await source.ReadAsync(chunk, ct)) > 0)
+        {
+            await buffer.WriteAsync(chunk.AsMemory(0, read), ct);
+            readSoFar += read;
+            if (totalBytes is > 0)
+                progress?.Report(Math.Min(DownloadProgressShare, (double)readSoFar / totalBytes.Value * DownloadProgressShare));
+        }
+
+        return buffer.ToArray();
+    }
+}
diff --git a/src/LageBuch.AppLogic/ViewModels/EinsatzgebietSection.cs b/src/LageBuch.AppLogic/ViewModels/EinsatzgebietSection.cs
index 72b7e12..ff4f68b 100644
--- a/src/LageBuch.AppLogic/ViewModels/EinsatzgebietSection.cs
+++ b/src/LageBuch.AppLogic/ViewModels/EinsatzgebietSection.cs
@@ -1,21 +1,31 @@
+using System.Collections.ObjectModel;
 using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using LageBuch.AppLogic.Services;
 using LageBuch.Persistence.MasterData;
 
 namespace LageBuch.AppLogic.ViewModels;
 
 /// <summary>
-/// Editor for the Wasserförderung region of operation (#150 phase 2): a name and a folder path
-/// expected to hold <c>region.mbtiles</c> and <c>region.dem</c>. Two scalar strings, so this
-/// mirrors <see cref="SettingsSection"/>'s pattern rather than the list sections' — one bindable
-/// property each, reporting through the shared dirty callback.
+/// Editor for the Wasserförderung region of operation (#150 phase 2, region-pack follow-up):
+/// a name and a folder path expected to hold <c>region.mbtiles</c> and <c>region.dem</c>.
+/// Primarily populated by downloading a published pack from <see cref="IRegionPackCatalogService"/>
+/// via <see cref="IRegionPackInstaller"/> — manual <see cref="Name"/>/<see cref="FolderPath"/> entry
+/// stays available as a fallback for a self-built or hand-placed pack.
 /// </summary>
 public sealed partial class EinsatzgebietSection : EditorSection
 {
     private readonly Action _onChanged;
+    private readonly IRegionPackCatalogService _catalog;
+    private readonly IRegionPackInstaller _installer;
 
-    public EinsatzgebietSection(string title, Einsatzgebiet einsatzgebiet, Action onChanged) : base(title)
+    public EinsatzgebietSection(
+        string title, Einsatzgebiet einsatzgebiet, Action onChanged,
+        IRegionPackCatalogService catalog, IRegionPackInstaller installer) : base(title)
     {
         _onChanged = onChanged;
+        _catalog = catalog;
+        _installer = installer;
         _name = einsatzgebiet.Name;
         _folderPath = einsatzgebiet.FolderPath;
     }
@@ -24,10 +34,81 @@ public EinsatzgebietSection(string title, Einsatzgebiet einsatzgebiet, Action on
     private string _name = string.Empty;
 
     [ObservableProperty]
+    [NotifyPropertyChangedFor(nameof(KartendatenGefunden))]
+    [NotifyPropertyChangedFor(nameof(KartendatenStatus))]
     private string _folderPath = string.Empty;
 
     partial void OnNameChanged(string value) => _onChanged();
     partial void OnFolderPathChanged(string value) => _onChanged();
 
     public Einsatzgebiet ToEinsatzgebiet() => new(Name, FolderPath);
+
+    // --- Region-pack catalog / download ---
+
+    public ObservableCollection<RegionPackInfo> AvailableRegions { get; } = new();
+
+    [ObservableProperty]
+    private RegionPackInfo? _selectedRegion;
+
+    [ObservableProperty]
+    private string? _catalogStatus;
+
+    [ObservableProperty]
+    private double _downloadProgress;
+
+    [RelayCommand]
+    private async Task LoadCatalog()
+    {
+        var regions = await _catalog.GetAvailableRegionsAsync();
+        AvailableRegions.Clear();
+        foreach (var region in regions)
+            AvailableRegions.Add(region);
+
+        CatalogStatus = AvailableRegions.Count == 0
+            ? "Keine Regionen verfügbar — bitte Internetverbindung prüfen, oder Ordner manuell angeben."
+            : null;
+    }
+
+    private bool CanDownloadSelectedRegion => SelectedRegion is not null;
+
+    [RelayCommand(CanExecute = nameof(CanDownloadSelectedRegion))]
+    private async Task DownloadSelectedRegion()
+    {
+        var region = SelectedRegion!;
+        DownloadProgress = 0;
+        var progress = new Progress<double>(p => DownloadProgress = p);
+        var folder = await _installer.DownloadAndInstallAsync(region, progress);
+
+        Name = region.Name;
+        FolderPath = folder;
+        _onChanged();
+    }
+
+    partial void OnSelectedRegionChanged(RegionPackInfo? value) => DownloadSelectedRegionCommand.NotifyCanExecuteChanged();
+
+    // --- File-presence validation: is region.mbtiles/region.dem actually at FolderPath? ---
+
+    public bool KartendatenGefunden =>
+        !string.IsNullOrWhiteSpace(FolderPath)
+        && File.Exists(Path.Combine(FolderPath, "region.mbtiles"))
+        && File.Exists(Path.Combine(FolderPath, "region.dem"));
+
+    public string? KartendatenStatus
+    {
+        get
+        {
+            if (string.IsNullOrWhiteSpace(FolderPath))
+                return null;
+
+            var mbtilesFound = File.Exists(Path.Combine(FolderPath, "region.mbtiles"));
+            var demFound = File.Exists(Path.Combine(FolderPath, "region.dem"));
+            if (mbtilesFound && demFound)
+                return "✓ Kartendaten gefunden.";
+
+            var missing = new List<string>();
+            if (!mbtilesFound) missing.Add("region.mbtiles");
+            if (!demFound) missing.Add("region.dem");
+            return $"✗ Fehlt: {string.Join(", ", missing)}.";
+        }
+    }
 }
diff --git a/src/LageBuch.AppLogic/ViewModels/MasterDataEditorViewModel.cs b/src/LageBuch.AppLogic/ViewModels/MasterDataEditorViewModel.cs
index a8d7cb4..a210e7d 100644
--- a/src/LageBuch.AppLogic/ViewModels/MasterDataEditorViewModel.cs
+++ b/src/LageBuch.AppLogic/ViewModels/MasterDataEditorViewModel.cs
@@ -17,6 +17,8 @@ public sealed partial class MasterDataEditorViewModel : ObservableObject
     private readonly IMasterDataProvider _provider;
     private readonly IFileDialogService _dialogs;
     private readonly IMasterDataFileService _files;
+    private readonly IRegionPackCatalogService _regionCatalog;
+    private readonly IRegionPackInstaller _regionInstaller;
     private MasterDataSet _original = MasterDataSet.Empty;
     private bool _originalIsEmpty = true;
 
@@ -30,11 +32,15 @@ public sealed partial class MasterDataEditorViewModel : ObservableObject
     private SettingsSection _settings = null!;
     private EinsatzgebietSection _einsatzgebiet = null!;
 
-    public MasterDataEditorViewModel(IMasterDataProvider provider, IFileDialogService dialogs, IMasterDataFileService files)
+    public MasterDataEditorViewModel(
+        IMasterDataProvider provider, IFileDialogService dialogs, IMasterDataFileService files,
+        IRegionPackCatalogService regionCatalog, IRegionPackInstaller regionInstaller)
     {
         _provider = provider;
         _dialogs = dialogs;
         _files = files;
+        _regionCatalog = regionCatalog;
+        _regionInstaller = regionInstaller;
         Load();
     }
 
@@ -100,7 +106,9 @@ private void PopulateSections(MasterDataSet set)
         Sections.Add(_checklistAbbau = new ChecklistTemplateSection("Checkliste Abbau", set.ChecklistTemplateAbbau, MarkDirty));
         Sections.Add(_personnel = new PersonnelSection("Personal", set.Personnel, MarkDirty));
         Sections.Add(_vehicles = new VehiclesSection("Fahrzeuge", set.Vehicles, set.Brigades, set.RadioCallSigns, OnVehiclesChanged));
-        Sections.Add(_einsatzgebiet = new EinsatzgebietSection("Einsatzgebiet", set.Einsatzgebiet, MarkDirty));
+        Sections.Add(_einsatzgebiet = new EinsatzgebietSection(
+            "Einsatzgebiet", set.Einsatzgebiet, MarkDirty, _regionCatalog, _regionInstaller));
+        _einsatzgebiet.LoadCatalogCommand.Execute(null);
 
         SelectedSection = Sections[Math.Clamp(previousIndex < 0 ? 0 : previousIndex, 0, Sections.Count - 1)];
     }
diff --git a/tests/LageBuch.Acceptance.Tests/AboutRenderTests.cs b/tests/LageBuch.Acceptance.Tests/AboutRenderTests.cs
index dfd56d1..7a9f813 100644
--- a/tests/LageBuch.Acceptance.Tests/AboutRenderTests.cs
+++ b/tests/LageBuch.Acceptance.Tests/AboutRenderTests.cs
@@ -93,7 +93,7 @@ private static MainWindowViewModel BuildMainWindowViewModel()
         var home = new HomeViewModel(new FakeStore(), masterData,
             new EmptyRecent(), dialogs, new FixedClock(), new NoopTicker(), new NoopAlarmService(),
             new NoopIncidentHostController(), "0.1.0");
-        var editor = new MasterDataEditorViewModel(masterData, dialogs, new NoFiles());
+        var editor = new MasterDataEditorViewModel(masterData, dialogs, new NoFiles(), new NoRegionCatalog(), new NoRegionInstaller());
         return new MainWindowViewModel(home, editor, dialogs, "0.1.0");
     }
 
@@ -109,6 +109,18 @@ private sealed class NoFiles : IMasterDataFileService
         public void Write(string path, MasterDataSet set) { }
     }
 
+    private sealed class NoRegionCatalog : IRegionPackCatalogService
+    {
+        public Task<IReadOnlyList<RegionPackInfo>> GetAvailableRegionsAsync(CancellationToken ct = default) =>
+            Task.FromResult<IReadOnlyList<RegionPackInfo>>(Array.Empty<RegionPackInfo>());
+    }
+
+    private sealed class NoRegionInstaller : IRegionPackInstaller
+    {
+        public Task<string> DownloadAndInstallAsync(RegionPackInfo pack, IProgress<double>? progress, CancellationToken ct = default) =>
+            Task.FromResult(string.Empty);
+    }
+
     private sealed class EmptyRecent : IRecentFilesStore
     {
         private readonly List<string> _list = new();
diff --git a/tests/LageBuch.Acceptance.Tests/MasterDataEditorRenderTests.cs b/tests/LageBuch.Acceptance.Tests/MasterDataEditorRenderTests.cs
index d294d42..de9f816 100644
--- a/tests/LageBuch.Acceptance.Tests/MasterDataEditorRenderTests.cs
+++ b/tests/LageBuch.Acceptance.Tests/MasterDataEditorRenderTests.cs
@@ -51,10 +51,22 @@ private sealed class NoFiles : IMasterDataFileService
         public void Write(string path, MasterDataSet set) { }
     }
 
+    private sealed class NoRegionCatalog : IRegionPackCatalogService
+    {
+        public Task<IReadOnlyList<RegionPackInfo>> GetAvailableRegionsAsync(CancellationToken ct = default) =>
+            Task.FromResult<IReadOnlyList<RegionPackInfo>>(Array.Empty<RegionPackInfo>());
+    }
+
+    private sealed class NoRegionInstaller : IRegionPackInstaller
+    {
+        public Task<string> DownloadAndInstallAsync(RegionPackInfo pack, IProgress<double>? progress, CancellationToken ct = default) =>
+            Task.FromResult(string.Empty);
+    }
+
     [AvaloniaFact]
     public void The_editor_renders_with_every_category()
     {
-        var vm = new MasterDataEditorViewModel(new SampleProvider(), new FakeDialogs(), new NoFiles());
+        var vm = new MasterDataEditorViewModel(new SampleProvider(), new FakeDialogs(), new NoFiles(), new NoRegionCatalog(), new NoRegionInstaller());
         var view = new MasterDataEditorView { DataContext = vm };
         var window = new Window { Content = view, Width = 1080, Height = 680 };
         window.Show();
@@ -80,7 +92,7 @@ public void The_editor_renders_with_every_category()
     [AvaloniaFact]
     public void Checkliste_aufbau_section_renders_text_and_mandatory_checkbox_per_row()
     {
-        var vm = new MasterDataEditorViewModel(new SampleProvider(), new FakeDialogs(), new NoFiles());
+        var vm = new MasterDataEditorViewModel(new SampleProvider(), new FakeDialogs(), new NoFiles(), new NoRegionCatalog(), new NoRegionInstaller());
         vm.SelectedSection = vm.Sections.Single(s => s.Title == "Checkliste Aufbau");
         var view = new MasterDataEditorView { DataContext = vm };
         var window = new Window { Content = view, Width = 1080, Height = 680 };
@@ -104,7 +116,7 @@ public void Checkliste_aufbau_section_renders_text_and_mandatory_checkbox_per_ro
     [AvaloniaFact]
     public void Links_section_renders_name_and_url_per_row()
     {
-        var vm = new MasterDataEditorViewModel(new SampleProvider(), new FakeDialogs(), new NoFiles());
+        var vm = new MasterDataEditorViewModel(new SampleProvider(), new FakeDialogs(), new NoFiles(), new NoRegionCatalog(), new NoRegionInstaller());
         vm.SelectedSection = vm.Sections.Single(s => s.Title == "Links");
         var view = new MasterDataEditorView { DataContext = vm };
         var window = new Window { Content = view, Width = 1080, Height = 680 };
@@ -127,7 +139,7 @@ public void Links_section_renders_name_and_url_per_row()
     [AvaloniaFact]
     public void Fahrzeuge_section_renders_wache_callsign_and_seats_per_row()
     {
-        var vm = new MasterDataEditorViewModel(new SampleProvider(), new FakeDialogs(), new NoFiles());
+        var vm = new MasterDataEditorViewModel(new SampleProvider(), new FakeDialogs(), new NoFiles(), new NoRegionCatalog(), new NoRegionInstaller());
         var section = (VehiclesSection)vm.Sections.Single(s => s.Title == "Fahrzeuge");
         section.AddCommand.Execute(null);
         section.Rows[0].Wache = "FFB Wache 1";
@@ -158,4 +170,51 @@ public void Fahrzeuge_section_renders_wache_callsign_and_seats_per_row()
         using var frame = window.CaptureRenderedFrame()!;
         frame.SavePng(Path.Combine(dir, "master-data-editor-fahrzeuge-after.png"));
     }
+
+    private sealed class FakeRegionCatalog(IReadOnlyList<RegionPackInfo> regions) : IRegionPackCatalogService
+    {
+        public Task<IReadOnlyList<RegionPackInfo>> GetAvailableRegionsAsync(CancellationToken ct = default) =>
+            Task.FromResult(regions);
+    }
+
+    // #150 follow-up (downloadable region packs): a dropdown lists the published catalog, and
+    // the old manual-folder fields collapse behind "Erweitert" instead of being the primary path.
+    [AvaloniaFact]
+    public void Einsatzgebiet_section_renders_region_dropdown_with_advanced_fields_collapsed()
+    {
+        var pack = new RegionPackInfo(
+            "Landkreis Fürstenfeldbruck", "ffb", "https://example.org/ffb.zip", 12_345_678,
+            48.0877067, 10.9930275, 48.2967233, 11.4128816, "2026-09-01",
+            "© OpenStreetMap contributors (ODbL). Höhendaten: SRTM (NASA/USGS, gemeinfrei).");
+        var vm = new MasterDataEditorViewModel(new SampleProvider(), new FakeDialogs(), new NoFiles(),
+            new FakeRegionCatalog(new[] { pack }), new NoRegionInstaller());
+        vm.SelectedSection = vm.Sections.Single(s => s.Title == "Einsatzgebiet");
+        var view = new MasterDataEditorView { DataContext = vm };
+        var window = new Window { Content = view, Width = 1080, Height = 680 };
+        window.Show();
+        Dispatcher.UIThread.RunJobs();
+
+        var comboBox = view.GetVisualDescendants().OfType<ComboBox>().Single(c => c.Name == "RegionComboBox");
+        Assert.Single(comboBox.ItemsSource!.Cast<object>());
+
+        var expander = view.GetVisualDescendants().OfType<Expander>().Single();
+        Assert.False(expander.IsExpanded);
+
+        var dir = Path.Combine(Path.GetTempPath(), "lagebuch-shots");
+        Directory.CreateDirectory(dir);
+        using var frame = window.CaptureRenderedFrame()!;
+        frame.SavePng(Path.Combine(dir, "master-data-editor-einsatzgebiet-collapsed.png"));
+
+        // Expand "Erweitert" and re-capture: the manual Name/Ordner fields are still there.
+        expander.IsExpanded = true;
+        Dispatcher.UIThread.RunJobs();
+        var textBoxes = view.GetVisualDescendants().OfType<TextBox>()
+            .Where(t => t.PlaceholderText is not null &&
+                (t.PlaceholderText.Contains("Fürstenfeldbruck") || t.PlaceholderText.Contains("/regions/ffb")))
+            .ToList();
+        Assert.Equal(2, textBoxes.Count);
+
+        using var expandedFrame = window.CaptureRenderedFrame()!;
+        expandedFrame.SavePng(Path.Combine(dir, "master-data-editor-einsatzgebiet-expanded.png"));
+    }
 }
diff --git a/tests/LageBuch.AppLogic.Tests/EinsatzgebietSectionTests.cs b/tests/LageBuch.AppLogic.Tests/EinsatzgebietSectionTests.cs
new file mode 100644
index 0000000..b41ab57
--- /dev/null
+++ b/tests/LageBuch.AppLogic.Tests/EinsatzgebietSectionTests.cs
@@ -0,0 +1,169 @@
+using LageBuch.AppLogic.Services;
+using LageBuch.AppLogic.ViewModels;
+using LageBuch.Persistence.MasterData;
+
+namespace LageBuch.AppLogic.Tests;
+
+public class EinsatzgebietSectionTests : IDisposable
+{
+    private readonly List<string> _tempDirs = new();
+
+    public void Dispose()
+    {
+        foreach (var dir in _tempDirs)
+            if (Directory.Exists(dir)) Directory.Delete(dir, recursive: true);
+    }
+
+    private string NewTempDir()
+    {
+        var dir = Path.Combine(Path.GetTempPath(), $"einsatzgebiet-{Guid.NewGuid():N}");
+        Directory.CreateDirectory(dir);
+        _tempDirs.Add(dir);
+        return dir;
+    }
+
+    private static readonly RegionPackInfo Ffb = new(
+        "Landkreis Fürstenfeldbruck", "ffb", "https://example.org/ffb.zip", 42,
+        48.08, 10.99, 48.29, 11.41, "2026-09-01", "© OpenStreetMap contributors (ODbL)");
+
+    private sealed class FakeCatalog(IReadOnlyList<RegionPackInfo> regions) : IRegionPackCatalogService
+    {
+        public Task<IReadOnlyList<RegionPackInfo>> GetAvailableRegionsAsync(CancellationToken ct = default)
+            => Task.FromResult(regions);
+    }
+
+    private sealed class FakeInstaller(string installedFolder) : IRegionPackInstaller
+    {
+        public RegionPackInfo? LastInstalled { get; private set; }
+
+        public Task<string> DownloadAndInstallAsync(RegionPackInfo pack, IProgress<double>? progress, CancellationToken ct = default)
+        {
+            LastInstalled = pack;
+            progress?.Report(0.5);
+            progress?.Report(1.0);
+            return Task.FromResult(installedFolder);
+        }
+    }
+
+    private static EinsatzgebietSection NewSection(
+        IRegionPackCatalogService? catalog = null, IRegionPackInstaller? installer = null, Action? onChanged = null) =>
+        new("Einsatzgebiet", Einsatzgebiet.Empty,
+            onChanged ?? (() => { }),
+            catalog ?? new FakeCatalog(Array.Empty<RegionPackInfo>()),
+            installer ?? new FakeInstaller("/tmp/unused"));
+
+    [Fact]
+    public async Task LoadCatalogCommand_populates_AvailableRegions_on_success()
+    {
+        var section = NewSection(catalog: new FakeCatalog(new[] { Ffb }));
+
+        await section.LoadCatalogCommand.ExecuteAsync(null);
+
+        Assert.Equal("ffb", Assert.Single(section.AvailableRegions).Slug);
+    }
+
+    [Fact]
+    public async Task LoadCatalogCommand_leaves_the_list_empty_and_sets_a_quiet_status_when_nothing_is_returned()
+    {
+        var section = NewSection(catalog: new FakeCatalog(Array.Empty<RegionPackInfo>()));
+
+        await section.LoadCatalogCommand.ExecuteAsync(null);
+
+        Assert.Empty(section.AvailableRegions);
+        Assert.NotNull(section.CatalogStatus);
+    }
+
+    [Fact]
+    public async Task DownloadSelectedRegionCommand_installs_the_selected_region_and_sets_name_and_folder()
+    {
+        var installedFolder = NewTempDir();
+        var installer = new FakeInstaller(installedFolder);
+        var section = NewSection(installer: installer);
+        section.SelectedRegion = Ffb;
+
+        await section.DownloadSelectedRegionCommand.ExecuteAsync(null);
+
+        Assert.Equal(Ffb, installer.LastInstalled);
+        Assert.Equal("Landkreis Fürstenfeldbruck", section.Name);
+        Assert.Equal(installedFolder, section.FolderPath);
+    }
+
+    [Fact]
+    public async Task DownloadSelectedRegionCommand_fires_the_dirty_callback()
+    {
+        var changedCount = 0;
+        var section = NewSection(installer: new FakeInstaller(NewTempDir()), onChanged: () => changedCount++);
+        section.SelectedRegion = Ffb;
+
+        await section.DownloadSelectedRegionCommand.ExecuteAsync(null);
+
+        Assert.True(changedCount > 0);
+    }
+
+    [Fact]
+    public void DownloadSelectedRegionCommand_cannot_execute_without_a_selected_region()
+    {
+        var section = NewSection();
+
+        Assert.False(section.DownloadSelectedRegionCommand.CanExecute(null));
+    }
+
+    [Fact]
+    public async Task DownloadSelectedRegionCommand_reports_progress_up_to_one()
+    {
+        var section = NewSection(installer: new FakeInstaller(NewTempDir()));
+        section.SelectedRegion = Ffb;
+
+        await section.DownloadSelectedRegionCommand.ExecuteAsync(null);
+
+        Assert.Equal(1.0, section.DownloadProgress);
+    }
+
+    // --- File-presence validation: is region.mbtiles/region.dem actually at FolderPath? ---
+
+    [Fact]
+    public void KartendatenStatus_is_null_when_folder_path_is_empty()
+    {
+        var section = NewSection();
+
+        Assert.Null(section.KartendatenStatus);
+        Assert.False(section.KartendatenGefunden);
+    }
+
+    [Fact]
+    public void KartendatenStatus_reports_both_files_missing()
+    {
+        var section = NewSection();
+        section.FolderPath = NewTempDir();
+
+        Assert.False(section.KartendatenGefunden);
+        Assert.Contains("region.mbtiles", section.KartendatenStatus);
+        Assert.Contains("region.dem", section.KartendatenStatus);
+    }
+
+    [Fact]
+    public void KartendatenStatus_names_only_the_missing_file_when_one_is_present()
+    {
+        var section = NewSection();
+        var dir = NewTempDir();
+        File.WriteAllText(Path.Combine(dir, "region.mbtiles"), "x");
+        section.FolderPath = dir;
+
+        Assert.False(section.KartendatenGefunden);
+        Assert.DoesNotContain("region.mbtiles", section.KartendatenStatus);
+        Assert.Contains("region.dem", section.KartendatenStatus);
+    }
+
+    [Fact]
+    public void KartendatenStatus_is_positive_when_both_files_are_present()
+    {
+        var section = NewSection();
+        var dir = NewTempDir();
+        File.WriteAllText(Path.Combine(dir, "region.mbtiles"), "x");
+        File.WriteAllText(Path.Combine(dir, "region.dem"), "x");
+        section.FolderPath = dir;
+
+        Assert.True(section.KartendatenGefunden);
+        Assert.NotNull(section.KartendatenStatus);
+    }
+}
diff --git a/tests/LageBuch.AppLogic.Tests/MainWindowViewModelTests.cs b/tests/LageBuch.AppLogic.Tests/MainWindowViewModelTests.cs
index bde7dc9..21844ad 100644
--- a/tests/LageBuch.AppLogic.Tests/MainWindowViewModelTests.cs
+++ b/tests/LageBuch.AppLogic.Tests/MainWindowViewModelTests.cs
@@ -39,7 +39,7 @@ public class MainWindowViewModelTests
     private static MainWindowViewModel New(IFileDialogService? dialogs = null)
     {
         var home = new HomeViewModel(new FakeStore(), new MvFakeMasterData(), new FakeRecent(), new FakeDialogs(), new FixedClock(T0), new FakeTicker(), new FakeAlarmService(), new NoopIncidentHostController(), "1.0.0");
-        return new MainWindowViewModel(home, new MasterDataEditorViewModel(new MvFakeMasterData(), new FakeDialogs(), new NoFiles()), dialogs ?? new FakeDialogs(), "0.1.0");
+        return new MainWindowViewModel(home, new MasterDataEditorViewModel(new MvFakeMasterData(), new FakeDialogs(), new NoFiles(), new NoRegionCatalog(), new NoRegionInstaller()), dialogs ?? new FakeDialogs(), "0.1.0");
     }
 
     [Fact]
@@ -97,7 +97,7 @@ public void RequestOpenFile_opens_readonly_without_prompt()
         var clock = new FixedClock(T0);
         LocalIncidentSession.StartNew(store, clock, new SessionOperator("Müller"), "/x.fwincident", Array.Empty<(string, bool)>(), Array.Empty<(string, bool)>());
         var home = new HomeViewModel(store, new MvFakeMasterData(), new FakeRecent(), new OpenPathDialogs(), clock, new FakeTicker(), new FakeAlarmService(), new NoopIncidentHostController(), "1.0.0");
-        var vm = new MainWindowViewModel(home, new MasterDataEditorViewModel(new MvFakeMasterData(), new FakeDialogs(), new NoFiles()), new FakeDialogs(), "0.1.0");
+        var vm = new MainWindowViewModel(home, new MasterDataEditorViewModel(new MvFakeMasterData(), new FakeDialogs(), new NoFiles(), new NoRegionCatalog(), new NoRegionInstaller()), new FakeDialogs(), "0.1.0");
 
         vm.RequestOpenFileCommand.Execute(null);
 
@@ -113,7 +113,7 @@ public void OpenRecent_opens_readonly_without_prompt()
         var clock = new FixedClock(T0);
         LocalIncidentSession.StartNew(store, clock, new SessionOperator("Müller"), "/x.fwincident", Array.Empty<(string, bool)>(), Array.Empty<(string, bool)>());
         var home = new HomeViewModel(store, new MvFakeMasterData(), new FakeRecent(), new FakeDialogs(), clock, new FakeTicker(), new FakeAlarmService(), new NoopIncidentHostController(), "1.0.0");
-        var vm = new MainWindowViewModel(home, new MasterDataEditorViewModel(new MvFakeMasterData(), new FakeDialogs(), new NoFiles()), new FakeDialogs(), "0.1.0");
+        var vm = new MainWindowViewModel(home, new MasterDataEditorViewModel(new MvFakeMasterData(), new FakeDialogs(), new NoFiles(), new NoRegionCatalog(), new NoRegionInstaller()), new FakeDialogs(), "0.1.0");
 
         vm.OpenRecent("/x.fwincident");
 
diff --git a/tests/LageBuch.AppLogic.Tests/MasterDataEditorViewModelTests.cs b/tests/LageBuch.AppLogic.Tests/MasterDataEditorViewModelTests.cs
index 58017b5..22ee4fb 100644
--- a/tests/LageBuch.AppLogic.Tests/MasterDataEditorViewModelTests.cs
+++ b/tests/LageBuch.AppLogic.Tests/MasterDataEditorViewModelTests.cs
@@ -69,7 +69,8 @@ public void Write(string path, MasterDataSet set)
 
     private static MasterDataEditorViewModel Vm(
         IMasterDataProvider provider, IFileDialogService? dialogs = null, IMasterDataFileService? files = null) =>
-        new(provider, dialogs ?? new FakeDialogs(), files ?? new FakeFileService());
+        new(provider, dialogs ?? new FakeDialogs(), files ?? new FakeFileService(),
+            new NoRegionCatalog(), new NoRegionInstaller());
 
     private static EditableListSection Roles(MasterDataEditorViewModel vm) =>
         vm.Sections.OfType<EditableListSection>().First(s => s.Title == "Rollen");
@@ -550,3 +551,17 @@ public void Fixing_the_duplicate_re_enables_saving()
         Assert.True(vm.SaveCommand.CanExecute(null));
     }
 }
+
+// Shared no-op fakes for constructor sites that don't exercise region-pack behavior — reused from
+// MainWindowViewModelTests.cs, same convention as FakeDialogs/FakeStore/etc.
+internal sealed class NoRegionCatalog : IRegionPackCatalogService
+{
+    public Task<IReadOnlyList<RegionPackInfo>> GetAvailableRegionsAsync(CancellationToken ct = default)
+        => Task.FromResult<IReadOnlyList<RegionPackInfo>>(Array.Empty<RegionPackInfo>());
+}
+
+internal sealed class NoRegionInstaller : IRegionPackInstaller
+{
+    public Task<string> DownloadAndInstallAsync(RegionPackInfo pack, IProgress<double>? progress, CancellationToken ct = default)
+        => Task.FromResult("/unused");
+}
diff --git a/tests/LageBuch.AppLogic.Tests/RegionPackCatalogJsonTests.cs b/tests/LageBuch.AppLogic.Tests/RegionPackCatalogJsonTests.cs
new file mode 100644
index 0000000..a9ea2d2
--- /dev/null
+++ b/tests/LageBuch.AppLogic.Tests/RegionPackCatalogJsonTests.cs
@@ -0,0 +1,115 @@
+using LageBuch.AppLogic.Services;
+
+namespace LageBuch.AppLogic.Tests;
+
+public class RegionPackCatalogJsonTests
+{
+    [Fact]
+    public void Parse_reads_every_field_of_a_valid_manifest()
+    {
+        var json = """
+            [
+              {
+                "name": "Landkreis Fürstenfeldbruck",
+                "slug": "ffb",
+                "downloadUrl": "https://example.org/ffb.zip",
+                "sizeBytes": 12345678,
+                "boundingBox": { "minLat": 48.0877067, "minLon": 10.9930275, "maxLat": 48.2967233, "maxLon": 11.4128816 },
+                "builtAt": "2026-09-01",
+                "attribution": "© OpenStreetMap contributors (ODbL). Elevation: SRTM (NASA/USGS, public domain)."
+              }
+            ]
+            """;
+
+        var regions = RegionPackCatalogJson.Parse(json);
+
+        var ffb = Assert.Single(regions);
+        Assert.Equal("Landkreis Fürstenfeldbruck", ffb.Name);
+        Assert.Equal("ffb", ffb.Slug);
+        Assert.Equal("https://example.org/ffb.zip", ffb.DownloadUrl);
+        Assert.Equal(12345678, ffb.SizeBytes);
+        Assert.Equal(48.0877067, ffb.MinLat);
+        Assert.Equal(10.9930275, ffb.MinLon);
+        Assert.Equal(48.2967233, ffb.MaxLat);
+        Assert.Equal(11.4128816, ffb.MaxLon);
+        Assert.Equal("2026-09-01", ffb.BuiltAt);
+        Assert.Contains("OpenStreetMap", ffb.Attribution);
+    }
+
+    [Fact]
+    public void Parse_reads_multiple_entries_in_order()
+    {
+        var json = """
+            [
+              { "name": "A", "slug": "a", "downloadUrl": "https://x/a.zip", "sizeBytes": 1,
+                "boundingBox": { "minLat": 0, "minLon": 0, "maxLat": 1, "maxLon": 1 },
+                "builtAt": "2026-01-01", "attribution": "x" },
+              { "name": "B", "slug": "b", "downloadUrl": "https://x/b.zip", "sizeBytes": 2,
+                "boundingBox": { "minLat": 0, "minLon": 0, "maxLat": 1, "maxLon": 1 },
+                "builtAt": "2026-01-02", "attribution": "x" }
+            ]
+            """;
+
+        var regions = RegionPackCatalogJson.Parse(json);
+
+        Assert.Equal(new[] { "a", "b" }, regions.Select(r => r.Slug));
+    }
+
+    [Theory]
+    [InlineData("")]
+    [InlineData("not json")]
+    [InlineData("{}")]
+    [InlineData("""[{"name": "Missing required fields"}]""")]
+    public void Parse_never_throws_and_returns_empty_for_malformed_input(string malformed)
+    {
+        var regions = RegionPackCatalogJson.Parse(malformed);
+
+        Assert.Empty(regions);
+    }
+
+    [Fact]
+    public void Parse_of_an_empty_array_returns_an_empty_list()
+        => Assert.Empty(RegionPackCatalogJson.Parse("[]"));
+
+    // The manifest is fetched from a third-party-controlled URL and its slug ends up as a path
+    // component (RegionPackInstaller extracts to <regionsBaseDir>/<slug>) — an entry with a
+    // path-traversal slug like "../../etc" must be rejected rather than silently accepted.
+    [Theory]
+    [InlineData("../evil")]
+    [InlineData("..\\evil")]
+    [InlineData("a/b")]
+    [InlineData("a\\b")]
+    [InlineData("")]
+    [InlineData("UPPER")]
+    [InlineData(".")]
+    public void Parse_rejects_entries_with_an_unsafe_slug(string unsafeSlug)
+    {
+        var json = $$"""
+            [
+              { "name": "Evil", "slug": "{{unsafeSlug.Replace("\\", "\\\\")}}", "downloadUrl": "https://x/e.zip", "sizeBytes": 1,
+                "boundingBox": { "minLat": 0, "minLon": 0, "maxLat": 1, "maxLon": 1 },
+                "builtAt": "2026-01-01", "attribution": "x" }
+            ]
+            """;
+
+        Assert.Empty(RegionPackCatalogJson.Parse(json));
+    }
+
+    [Theory]
+    [InlineData("ffb")]
+    [InlineData("landkreis-ffb")]
+    [InlineData("region_1")]
+    [InlineData("a")]
+    public void Parse_accepts_entries_with_a_safe_slug(string safeSlug)
+    {
+        var json = $$"""
+            [
+              { "name": "OK", "slug": "{{safeSlug}}", "downloadUrl": "https://x/ok.zip", "sizeBytes": 1,
+                "boundingBox": { "minLat": 0, "minLon": 0, "maxLat": 1, "maxLon": 1 },
+                "builtAt": "2026-01-01", "attribution": "x" }
+            ]
+            """;
+
+        Assert.Equal(safeSlug, Assert.Single(RegionPackCatalogJson.Parse(json)).Slug);
+    }
+}
diff --git a/tests/LageBuch.AppLogic.Tests/RegionPackCatalogServiceTests.cs b/tests/LageBuch.AppLogic.Tests/RegionPackCatalogServiceTests.cs
new file mode 100644
index 0000000..cacce1e
--- /dev/null
+++ b/tests/LageBuch.AppLogic.Tests/RegionPackCatalogServiceTests.cs
@@ -0,0 +1,73 @@
+using System.Net;
+using LageBuch.AppLogic.Services;
+
+namespace LageBuch.AppLogic.Tests;
+
+public class RegionPackCatalogServiceTests
+{
+    private sealed class FakeHandler(Func<HttpRequestMessage, HttpResponseMessage> respond) : HttpMessageHandler
+    {
+        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken ct)
+            => Task.FromResult(respond(request));
+    }
+
+    private static readonly string ValidManifest = """
+        [
+          { "name": "Landkreis Fürstenfeldbruck", "slug": "ffb", "downloadUrl": "https://example.org/ffb.zip",
+            "sizeBytes": 42, "boundingBox": { "minLat": 48.08, "minLon": 10.99, "maxLat": 48.29, "maxLon": 11.41 },
+            "builtAt": "2026-09-01", "attribution": "OSM" }
+        ]
+        """;
+
+    [Fact]
+    public async Task GetAvailableRegionsAsync_returns_the_parsed_manifest_on_success()
+    {
+        var handler = new FakeHandler(_ => new HttpResponseMessage(HttpStatusCode.OK)
+        {
+            Content = new StringContent(ValidManifest),
+        });
+        var service = new RegionPackCatalogService(new HttpClient(handler), "https://example.org/regions.json");
+
+        var regions = await service.GetAvailableRegionsAsync();
+
+        Assert.Equal("ffb", Assert.Single(regions).Slug);
+    }
+
+    [Fact]
+    public async Task GetAvailableRegionsAsync_fetches_the_configured_manifest_url()
+    {
+        HttpRequestMessage? seenRequest = null;
+        var handler = new FakeHandler(r =>
+        {
+            seenRequest = r;
+            return new HttpResponseMessage(HttpStatusCode.OK) { Content = new StringContent("[]") };
+        });
+        var service = new RegionPackCatalogService(new HttpClient(handler), "https://example.org/regions.json");
+
+        await service.GetAvailableRegionsAsync();
+
+        Assert.Equal("https://example.org/regions.json", seenRequest?.RequestUri?.ToString());
+    }
+
+    [Fact]
+    public async Task GetAvailableRegionsAsync_returns_empty_list_never_throws_on_http_failure()
+    {
+        var handler = new FakeHandler(_ => new HttpResponseMessage(HttpStatusCode.NotFound));
+        var service = new RegionPackCatalogService(new HttpClient(handler), "https://example.org/regions.json");
+
+        var regions = await service.GetAvailableRegionsAsync();
+
+        Assert.Empty(regions);
+    }
+
+    [Fact]
+    public async Task GetAvailableRegionsAsync_returns_empty_list_never_throws_when_the_handler_throws()
+    {
+        var handler = new FakeHandler(_ => throw new HttpRequestException("no route to host"));
+        var service = new RegionPackCatalogService(new HttpClient(handler), "https://example.org/regions.json");
+
+        var regions = await service.GetAvailableRegionsAsync();
+
+        Assert.Empty(regions);
+    }
+}
diff --git a/tests/LageBuch.AppLogic.Tests/RegionPackInstallerTests.cs b/tests/LageBuch.AppLogic.Tests/RegionPackInstallerTests.cs
new file mode 100644
index 0000000..76822cb
--- /dev/null
+++ b/tests/LageBuch.AppLogic.Tests/RegionPackInstallerTests.cs
@@ -0,0 +1,109 @@
+using System.IO.Compression;
+using System.Net;
+using LageBuch.AppLogic.Services;
+
+namespace LageBuch.AppLogic.Tests;
+
+public class RegionPackInstallerTests : IDisposable
+{
+    private readonly string _regionsBaseDir = Path.Combine(Path.GetTempPath(), $"regions-{Guid.NewGuid():N}");
+
+    public void Dispose()
+    {
+        if (Directory.Exists(_regionsBaseDir))
+            Directory.Delete(_regionsBaseDir, recursive: true);
+    }
+
+    private sealed class FakeHandler(Func<HttpRequestMessage, HttpResponseMessage> respond) : HttpMessageHandler
+    {
+        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken ct)
+            => Task.FromResult(respond(request));
+    }
+
+    private static byte[] BuildFakePackZip(string mbtilesContent = "fake-mbtiles", string demContent = "fake-dem")
+    {
+        using var ms = new MemoryStream();
+        using (var zip = new ZipArchive(ms, ZipArchiveMode.Create, leaveOpen: true))
+        {
+            using (var entry = zip.CreateEntry("region.mbtiles").Open())
+            using (var writer = new StreamWriter(entry))
+                writer.Write(mbtilesContent);
+            using (var entry = zip.CreateEntry("region.dem").Open())
+            using (var writer = new StreamWriter(entry))
+                writer.Write(demContent);
+        }
+        return ms.ToArray();
+    }
+
+    private static RegionPackInfo FfbPack(string downloadUrl = "https://example.org/ffb.zip") => new(
+        "Landkreis Fürstenfeldbruck", "ffb", downloadUrl, 42, 48.08, 10.99, 48.29, 11.41, "2026-09-01", "OSM");
+
+    [Fact]
+    public async Task DownloadAndInstallAsync_extracts_the_zip_into_a_slug_named_folder()
+    {
+        var handler = new FakeHandler(_ => new HttpResponseMessage(HttpStatusCode.OK)
+        {
+            Content = new ByteArrayContent(BuildFakePackZip()),
+        });
+        var installer = new RegionPackInstaller(new HttpClient(handler), _regionsBaseDir);
+
+        var folder = await installer.DownloadAndInstallAsync(FfbPack(), progress: null);
+
+        Assert.Equal(Path.Combine(_regionsBaseDir, "ffb"), folder);
+        Assert.Equal("fake-mbtiles", await File.ReadAllTextAsync(Path.Combine(folder, "region.mbtiles")));
+        Assert.Equal("fake-dem", await File.ReadAllTextAsync(Path.Combine(folder, "region.dem")));
+    }
+
+    [Fact]
+    public async Task DownloadAndInstallAsync_requests_the_packs_download_url()
+    {
+        HttpRequestMessage? seenRequest = null;
+        var handler = new FakeHandler(r =>
+        {
+            seenRequest = r;
+            return new HttpResponseMessage(HttpStatusCode.OK) { Content = new ByteArrayContent(BuildFakePackZip()) };
+        });
+        var installer = new RegionPackInstaller(new HttpClient(handler), _regionsBaseDir);
+
+        await installer.DownloadAndInstallAsync(FfbPack("https://example.org/specific-ffb.zip"), progress: null);
+
+        Assert.Equal("https://example.org/specific-ffb.zip", seenRequest?.RequestUri?.ToString());
+    }
+
+    [Fact]
+    public async Task DownloadAndInstallAsync_re_installing_the_same_slug_removes_stale_files()
+    {
+        var handler = new FakeHandler(_ => new HttpResponseMessage(HttpStatusCode.OK)
+        {
+            Content = new ByteArrayContent(BuildFakePackZip()),
+        });
+        var installer = new RegionPackInstaller(new HttpClient(handler), _regionsBaseDir);
+        var folder = await installer.DownloadAndInstallAsync(FfbPack(), progress: null);
+        var staleFile = Path.Combine(folder, "old-junk.txt");
+        await File.WriteAllTextAsync(staleFile, "leftover from a previous version");
+
+        await installer.DownloadAndInstallAsync(FfbPack(), progress: null);
+
+        Assert.False(File.Exists(staleFile));
+        Assert.True(File.Exists(Path.Combine(folder, "region.mbtiles")));
+    }
+
+    [Fact]
+    public async Task DownloadAndInstallAsync_reports_progress_from_zero_to_one()
+    {
+        var handler = new FakeHandler(_ => new HttpResponseMessage(HttpStatusCode.OK)
+        {
+            Content = new ByteArrayContent(BuildFakePackZip()),
+        });
+        var installer = new RegionPackInstaller(new HttpClient(handler), _regionsBaseDir);
+        var reported = new List<double>();
+        var progress = new Progress<double>(reported.Add);
+
+        await installer.DownloadAndInstallAsync(FfbPack(), progress);
+        // Progress<T> marshals via SynchronizationContext.Post when one is captured; without one
+        // (the xunit test-runner thread has none) it invokes synchronously, so this is deterministic.
+
+        Assert.NotEmpty(reported);
+        Assert.Equal(1.0, reported[^1]);
+    }
+}
diff --git a/tools/build-region-pack/README.md b/tools/build-region-pack/README.md
new file mode 100644
index 0000000..c05c425
--- /dev/null
+++ b/tools/build-region-pack/README.md
@@ -0,0 +1,157 @@
+# Building a Wasserförderung region pack
+
+This is a runbook, not an app component. It documents how a maintainer builds and publishes one
+region pack (one Landkreis) for the Wasserförderung "Karte" map mode (#150 follow-up). It is
+**deliberately not part of `LageBuch.sln`** — it doesn't ship with the app, doesn't run in the
+app's CI, and isn't built/tested by `dotnet build`/`dotnet test`. It's a manual, occasional process
+a maintainer runs on their own machine with real internet access, using off-the-shelf OSS tools.
+
+The app itself only ever *downloads* a pack someone already built this way — see
+`src/LageBuch.AppLogic/Services/IRegionPackCatalogService.cs` and `IRegionPackInstaller.cs`.
+
+## What a pack contains
+
+A zip with exactly two files at its root:
+
+- `region.mbtiles` — raster map tiles, standard MBTiles SQLite schema, TMS row numbering, zoom
+  11–15. Read by `src/LageBuch.AppLogic/Services/MbTilesFileSource.cs`.
+- `region.dem` — elevation grid in this app's own binary format ("FWDM"): little-endian header
+  (magic, version, origin lat/lon, cell-size-degrees, rows, cols) + row-major `Int16` body,
+  `-32768` = NoData. See `src/LageBuch.AppLogic/Services/DemFileElevationSampler.cs`'s doc comment
+  for the exact byte layout. SRTM's own Skadi `.hgt` format is nearly identical (same NoData
+  sentinel, same 1-arcsecond grid) — the only real conversion is a byte order swap and writing our
+  small header.
+
+## Licensing (read this before publishing anything)
+
+- **OpenStreetMap data (ODbL 1.0)**: rendered raster tiles are a "Produced Work", not a
+  "Derivative Database" — see the OSM Foundation's Legal FAQ. Produced Works need **attribution
+  only** ("© OpenStreetMap contributors", linking to the ODbL/copyright page); share-alike does
+  **not** apply. If a future pack ever ships raw/vector OSM data instead of flattened raster
+  images, revisit this — vector tiles with queryable attributes are much closer to a Derivative
+  Database and ODbL's share-alike would likely apply.
+- **SRTM elevation (NASA/USGS)**: US federal government work, public domain, freely
+  redistributable. No legal attribution requirement (a courtesy credit is still included below).
+- **Copernicus DEM**: higher resolution than SRTM and tempting as a future upgrade, but its exact
+  redistribution terms for derived/cropped public extracts have **not been confirmed**. Don't use
+  it for a published pack until someone has actually read the license and confirmed this is
+  permitted.
+- Every published pack's `regions.json` entry carries an `attribution` string (see below) that the
+  app surfaces directly under the installed region in Stammdaten → Einsatzgebiet. Keep that string
+  accurate for what the pack actually contains.
+
+## Prerequisites
+
+- [`osmium-tool`](https://osmcode.org/osmium-tool/) — extracts a bounded region from a larger
+  `.osm.pbf` without needing a database.
+- A raster tile renderer that reads `.osm`/`.pbf` directly and needs no database setup — e.g.
+  [Maperitive](http://maperitive.net/) (single executable, built-in default style) or
+  [Mapnik](https://mapnik.org/) + the classic `generate_tiles.py` script. Pin whichever is actually
+  available and maintained at the time you run this — don't assume either is still the best choice.
+- `sqlite3` CLI (to assemble/inspect the `.mbtiles` file — most tile renderers write this format
+  natively; if yours doesn't, `mbutil` converts a tile directory into one).
+- `curl` and `gzip` (SRTM `.hgt.gz` download).
+- A `.NET` SDK is **not** required for any of this — none of it touches `LageBuch.sln`.
+
+## 1. Find the region's exact boundary
+
+Look up the Landkreis's OSM relation and precise administrative boundary via Nominatim:
+
+```sh
+curl -s "https://nominatim.openstreetmap.org/lookup?osm_ids=R<relation-id>&format=json&polygon_geojson=1" \
+  -o boundary.json
+```
+
+For Landkreis Fürstenfeldbruck this is relation **62595**, bounding box
+**48.0877067,10.9930275 – 48.2967233,11.4128816**.
+
+## 2. Extract the region from a Geofabrik regional extract
+
+Download the containing regional `.osm.pbf` from [Geofabrik](https://download.geofabrik.de/)
+(e.g. `bayern-latest.osm.pbf` for a Bavarian Landkreis), then clip to the precise boundary:
+
+```sh
+osmium extract --polygon boundary.geojson bayern-latest.osm.pbf -o ffb.osm.pbf
+```
+
+(`boundary.geojson` is `boundary.json`'s `geojson` field extracted into its own file — osmium wants
+a bare GeoJSON polygon, not the full Nominatim response.)
+
+## 3. Render raster tiles, zoom 11–15
+
+Render directly from `ffb.osm.pbf` with whichever tool you picked above, output as a directory of
+`{z}/{x}/{y}.png` tiles or directly as MBTiles if the tool supports it. Zoom 11–15 is enough detail
+for route planning at Landkreis scale without an unreasonably large pack.
+
+## 4. Pack into `region.mbtiles`
+
+If your renderer didn't write MBTiles directly, pack the tile directory with `mbutil`:
+
+```sh
+mb-util --image_format=png tiles/ region.mbtiles
+```
+
+`MbTilesFileSource.cs` expects the standard schema (`tiles(zoom_level, tile_column, tile_row,
+tile_data)`) with **TMS row numbering** (row 0 = south) — this is what `mb-util` and most tile
+tools produce natively; no manual row-flipping should be needed.
+
+## 5. Build `region.dem` from SRTM
+
+Download the SRTM `.hgt.gz` tiles covering the bbox (+2 km padding) from the public
+`elevation-tiles-prod` S3 bucket:
+
+```sh
+curl -sO https://s3.amazonaws.com/elevation-tiles-prod/skadi/N48/N48E010.hgt.gz
+curl -sO https://s3.amazonaws.com/elevation-tiles-prod/skadi/N48/N48E011.hgt.gz
+gunzip N48E010.hgt.gz N48E011.hgt.gz
+```
+
+Mosaic adjacent tiles (de-duplicating the shared edge column/row between neighboring 1°×1° tiles),
+then convert to `region.dem`:
+
+- SRTM `.hgt` is big-endian `Int16`, 1 arcsecond/cell (3601×3601 per tile), `-32768` = void. Our
+  format is little-endian with the same cell size and the same NoData sentinel — no resampling
+  needed, just a byte-swap and prepending our 40-byte header (magic `FWDM`, version, origin
+  lat/lon, cell-size-degrees, row count, column count — see `DemFileElevationSampler.cs`).
+- `build-dem.py` (or equivalent) is intentionally left as a short script you write against the
+  exact header layout in that file at the time you run this — the format is simple enough that
+  hand-rolling a ~30-line converter beats depending on a library for a once-per-pack step.
+
+## 6. Zip and publish
+
+```sh
+zip ffb.zip region.mbtiles region.dem
+```
+
+Publish as a GitHub Release asset in the region-pack repo (recommended: a separate repo, e.g.
+`CodeForFire/lagebuch-regions`, kept apart from this app's own release history so a pack update is
+never confused with an app version) — one tag per pack, e.g. `ffb-v1`.
+
+Add (or update) the pack's entry in that repo's `regions.json`, served raw at
+`https://raw.githubusercontent.com/CodeForFire/lagebuch-regions/main/regions.json` (this exact URL
+is `CompositionRoot.RegionPackManifestUrl` in this repo — update both if the manifest ever moves):
+
+```json
+{
+  "name": "Landkreis Fürstenfeldbruck",
+  "slug": "ffb",
+  "downloadUrl": "https://github.com/CodeForFire/lagebuch-regions/releases/download/ffb-v1/ffb.zip",
+  "sizeBytes": 12345678,
+  "minLat": 48.0877067,
+  "minLon": 10.9930275,
+  "maxLat": 48.2967233,
+  "maxLon": 11.4128816,
+  "builtAt": "2026-09-01",
+  "attribution": "© OpenStreetMap contributors (ODbL). Höhendaten: SRTM (NASA/USGS, gemeinfrei)."
+}
+```
+
+The app fetches this manifest, lists every entry in the Stammdaten → Einsatzgebiet dropdown, and
+downloads/extracts whichever one the operator picks. No app code change is needed to publish a new
+region — only a `regions.json` update.
+
+## What this runbook does not cover
+
+Actually running these steps for Landkreis Fürstenfeldbruck (~244 MB regional extract, real tile
+rendering, real SRTM download) needs a machine with real internet access and takes a while — that's
+a manual follow-up outside this repo/session, not something covered by `dotnet test`.