Add geologic map layer

[akthom]

Can we add a geologic map layer to the globe? e.g. https://macrostrat.org/burwell/#3/40.80/-94.10

[rdhyee]

Feasibility: yes — cheap and well-suited to our stack

Macrostrat serves standard XYZ raster tiles (tiles.macrostrat.org/carto/{z}/{x}/{y}.png — verified reachable today), and Cesium overlays those natively (UrlTemplateImageryProvider + per-layer transparency). Implementation is essentially:

• add the Macrostrat layer as a translucent overlay (alpha ~0.5) above the base imagery,
• a checkbox/slider in the map panel to toggle it and control opacity,
• attribution (Macrostrat is CC-BY — credit line in the map's credit area),
• a smoke test.

Estimate: roughly a day including UI, attribution, and tests. Two design questions before building:

1. Default off, presumably (it visually competes with the sample dots)?
2. Only the carto blended layer, or also Macrostrat's scale-specific layers?

Pairs naturally with #324 — a 2D map + geologic overlay is the classic geologist's view.

— rbotyee 🤖 (Claude, Raymond's assistant)

[rdhyee]

@akthom gentle ping — the feasibility note above ended with two small design questions for you (default off? blended "carto" layer vs scale-specific layers?) but I failed to @-mention you, so you may never have been notified. Answers unblock ~a day of work. — rbotyee 🤖 (Claude, for @rdhyee)

[rdhyee]

🤖 rbotyee (Claude, operated by @rdhyee) — Raymond's intent: stop waiting on the two open design questions and unblock this (~a day of work); his answers below. What I did: posting the decisions; implementation to follow.

Answering the two questions from the feasibility note (Raymond's calls, 2026-07-17):

1. Default off — the geologic layer is opt-in via the layer control, so the Explorer's default look is unchanged.
2. All the layers, not a choice — rather than picking blended-carto or scale-specific, expose a small layer picker offering Macrostrat's blended carto layer plus the scale-specific ones. Default remains "off"; users choose.

@akthom if either of these conflicts with what you had in mind, say so and we'll adjust — otherwise this proceeds as scoped (~a day). — rbotyee 🤖 (Claude, for @rdhyee)