fix(fires): paint aggregated heat cells warm by density, not by strongest FRP

Coloring each far-zoom cell with the ramp stop of its strongest detection
turned a burning region into a blue / teal / lime mosaic: neighbouring
cells flipped hue on one outlier and the cold stops did not read as fire.
Cells say where it burns, so they go back to the heat-normalized score
(density, night share, max FRP) on the warm end of the ramp — lime, amber,
red — with the cell card accent matching. Single detections keep the full
six-stop FRP ramp.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

src/layers/firms/model.js

@@ -137,15 +137,33 @@ export function createModel({
   }
 
   /**
-   * Fill color for an aggregated heat cell: the ramp color of its strongest
-   * detection, so cells, markers and the slider legend read on one scale.
-   * @param {number} maxFrp - Strongest FRP in the cell, megawatts.
+   * Severity stop for an aggregated heat cell from its heat-normalized score
+   * (density, night share and strongest FRP together). Cells say *where* it
+   * burns, so they stay on the warm end of the ramp — lime, amber, red — and
+   * read as one field instead of a per-cell mosaic; the cold stops belong to
+   * single detections, which say *how hard* each one burns.
+   * @param {number} normalized - 0..1 heat score (sqrt-normalized to the view).
+   * @returns {{name: string, minFrp: number, color: Cesium.Color}}
+   */
+
+  function cellColorStop(normalized) {
+    const name =
+      normalized > 0.72 ? 'red' : normalized > 0.42 ? 'amber' : 'lime';
+    return (
+      DETECTION_COLOR_STOPS.find((stop) => stop.name === name) ||
+      DETECTION_COLOR_STOPS[0]
+    );
+  }
+
+  /**
+   * Fill color for an aggregated heat cell.
+   * @param {number} normalized - 0..1 heat score (see {@link cellColorStop}).
    * @param {number} alpha - Fill alpha (heat-normalized by the caller).
    * @returns {Cesium.Color}
    */
 
-  function heatColor(maxFrp, alpha) {
-    return frpColorStop(maxFrp).color.withAlpha(alpha);
+  function heatColor(normalized, alpha) {
+    return cellColorStop(normalized).color.withAlpha(alpha);
   }
 
   /**
@@ -476,14 +494,14 @@ export function createModel({
   }
 
   /**
-   * Cell card accent: the ramp stop of the cell's strongest detection,
+   * Cell card accent: the warm severity stop of the cell's heat score,
    * mirroring heatColor.
-   * @param {number} maxFrp - Strongest FRP in the cell, megawatts.
+   * @param {number} normalized - 0..1 heat score.
    * @returns {string} "r, g, b" accent string.
    */
 
-  function cellAccent(maxFrp) {
-    return accentForSeverity(frpColorStop(maxFrp).name);
+  function cellAccent(normalized) {
+    return accentForSeverity(cellColorStop(normalized).name);
   }
 
   /** Coordinate line like "30.512°N 75.831°E". */
@@ -590,6 +608,7 @@ export function createModel({
     cellIntersectsBounds,
     heatScore,
     heatColor,
+    cellColorStop,
     frpColorStop,
     detectionColorStop,
     frpPixelSize,

src/layers/firms/rendering.js

@@ -144,7 +144,7 @@ export function createRendering({
       const score = components.model.heatScore(cell);
       const normalized = Math.min(1, Math.sqrt(score / maxScore));
       const alpha = 0.16 + normalized * 0.5;
-      const color = components.model.heatColor(cell.maxFrp, alpha);
+      const color = components.model.heatColor(normalized, alpha);
       const centerLon = cell.lonCell + lod.gridDegrees / 2;
       const centerLat = cell.latCell + lod.gridDegrees / 2;
       const position = Cesium.Cartesian3.fromDegrees(centerLon, centerLat, 0);
@@ -170,12 +170,13 @@ export function createRendering({
       });
 
       // Cells arrive heat-sorted, so candidate order doubles as label priority.
+      // Accent is resolved here because `normalized` only exists in this walk.
       layerState._labelCandidates.push({
         position,
         cullPosition: components.model.cellCullPosition(centerLon, centerLat),
         fire: null,
         cell,
-        accent: components.model.cellAccent(cell.maxFrp),
+        accent: components.model.cellAccent(normalized),
       });
     }