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)