docs(fires): describe the far-zoom heatmap

Co-Authored-By: Claude Opus 5.5 <[email protected]>

changelog.d/1426-fire-intensity-filter.md

@@ -2,8 +2,8 @@
   cold → hot ramp (blue · teal · lime · amber · orange · red at 0 · 5 · 20 ·
   50 · 100 · 300 MW), and add a log-scale minimum-FRP slider whose track is the
   ramp, an All / Nominal+ / High confidence switch and an "N of M shown"
-  counter to the layer row. Far-zoom heat cells keep a warm density fill
-  (lime · amber · red). The filter applies once before rendering, so
-  markers, cards, heat cells, context and the top-fires query agree; share
+  counter to the layer row. Far zoom shows a Snap Map–style heatmap instead
+  of squares, empty where nothing burns. The filter applies once before
+  rendering, so markers, cards, the heatmap, context and the top-fires query agree; share
   links keep it (`w` token: `f`, `c`), and `get_active_fires` takes matching
   `min_frp_mw` and `confidence` arguments. Default 0 MW / All (gekh, #1426).

docs/CURRENT-STATE.md

@@ -2060,10 +2060,19 @@ Every FIRMS detection is colored by fire radiative power on a six-stop cold →
 hot ramp: blue from 0 MW, teal from 5, lime from 20, amber from 50, orange from
 100 and red from 300 MW (`FRP_RAMP` in `src/data/firmsIntensity.js`). Glow
 sprites and fire-card accents read that ramp; confidence and brightness do
-not affect the color. Aggregated heat cells (far zoom) instead take the warm
-end of the ramp — lime, amber or red — from their heat-normalized score
-(density, night share and strongest FRP), so a region reads as one field
-rather than a per-cell mosaic; the cell card's accent matches its fill.
+not affect the color.
+
+At far zoom (camera above ~3,000 km) the layer drapes a Snap Map–style
+heatmap instead of individual markers: the shown detections are binned on a
+global 2048 × 1024 grid, each weighted `1 + log10(1 + FRP)`, Gaussian-blurred,
+normalized on a log scale against the 99.5th percentile and mapped from blue
+through cyan, green, yellow and orange to red. Nothing is painted where
+nothing burns (`src/data/firmsHeatRaster.js`). It is one full-globe imagery
+tile on the active imagery host (`src/layers/firms/heatImagery.js`), rebuilt
+on each data refresh or filter change (the first paint at once, later ones
+150 ms after the last change) and hidden once markers take over below
+~750 km. "N FIRES" cards from a 2° / 1° aggregation still label the hottest
+areas; their accent is the strongest fire's FRP color.
 
 The Active Fires row carries a "Fire intensity (FRP)" slider on a log scale
 whose track is painted with the ramp and ticked at the same six values (its
@@ -2071,7 +2080,7 @@ value reads "All" or "≥ N MW"), a "Confidence" switch with All / Nominal+ /
 High, and an "N of M shown" counter. The default is 0 MW and
 All, because many of the strongest detections are rated low confidence. The
 filter runs once in `ingestion.applyFilter()` before rendering, so markers,
-cards, heat cells, the shared context store, the top-fires query and the
+cards, the heatmap, the shared context store, the top-fires query and the
 analyst records all see one filtered set; a selected fire that no longer passes
 is deselected. The layer state keeps both options under the `w` (`local-firms`)
 share token as `f` (whole megawatts, 0–10,000) and `c` (`a`, `n`, `h`),