Draw each far-zoom fire as a marker-sized heat spot

The heat raster was 2048 px wide with a 3 px blur, so every fire spread
over ~200 km and the far-zoom map read as clouds next to the markers.
Double the grid to ~10 km per pixel and blur by one pixel: a lone fire
is now a spot about as wide as its marker at the 3,000 km hand-off.

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

@@ -4,6 +4,6 @@
   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 shows a Snap Map–style heatmap in the same colors 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
+  one marker-sized spot per fire, 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

@@ -2185,9 +2185,10 @@ accents read that ramp; confidence and brightness do 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 by its FRP in megawatts (so heat is
+global 4096 × 2048 grid (≈10 km per pixel), each weighted by its FRP in megawatts (so heat is
 radiated power, and raising the FRP slider does not dim areas where strong fires
-burn), Gaussian-blurred,
+burn), Gaussian-blurred by one pixel so each fire stays a spot about the size
+of its marker,
 normalized on a log scale against the 99.5th percentile and mapped through the
 same hues, from a bright red edge through orange and gold to a pale
 white-hot core. The edge starts more than half opaque, so regions far below

src/layers/firms/heatImagery.test.mjs

@@ -1,6 +1,8 @@
 import test from 'node:test';
 import assert from 'node:assert/strict';
 import { createHeatImagery } from './heatImagery.js';
+import { buildHeatRaster } from '../../data/firmsHeatRaster.js';
+import { HEAT_RASTER } from './policy.js';
 
 function harness() {
   const layers = [];
@@ -85,3 +87,26 @@ test('destroy removes the layer', () => {
   h.imagery.destroy();
   assert.equal(h.layers.length, 0);
 });
+
+test('the shipped raster paints a lone weak fire as a marker-sized spot', () => {
+  // A hot cluster elsewhere sets the scale, as Africa does on real data.
+  const fires = [{ lat: 0, lon: 0, frp: 5 }];
+  for (let i = 0; i < 40; i++) {
+    fires.push({ lat: -10 + (i % 5) * 0.1, lon: 25 + i * 0.05, frp: 300 });
+  }
+  const r = buildHeatRaster(fires, HEAT_RASTER);
+  const y = Math.floor((90 / 180) * r.height);
+  const painted = [];
+  for (let x = 0; x < r.width; x++) {
+    const lon = ((x + 0.5) / r.width) * 360 - 180;
+    if (Math.abs(lon) < 5 && r.rgba[(y * r.width + x) * 4 + 3] > 0) {
+      painted.push(x);
+    }
+  }
+  const kmPerPx = 40075 / r.width;
+  assert.ok(painted.length > 0, 'the weak fire still shows');
+  assert.ok(
+    painted.length * kmPerPx <= 80,
+    `spot ${Math.round(painted.length * kmPerPx)} km wide`,
+  );
+});

src/layers/firms/policy.js

@@ -49,14 +49,17 @@ export const LOD_LEVELS = [
 ];
 
 /**
- * Global heat raster for the `heat` bands: ≈0.18° per pixel, Gaussian σ in
+ * Global heat raster for the `heat` bands: ≈0.09° (≈10 km) per pixel and a
- * pixels. Built once per data refresh or filter change, never per camera move.
+ * one-pixel Gaussian σ, so a lone fire is a spot about as wide as its marker
+ * at the 3,000 km hand-off and neighbours merge only when they really touch
+ * (2048 px with σ 3 smeared each fire over ~200 km). Built once per data
+ * refresh or filter change, never per camera move.
  */
 
 export const HEAT_RASTER = Object.freeze({
-  width: 2048,
+  width: 4096,
-  height: 1024,
+  height: 2048,
-  sigmaPx: 3,
+  sigmaPx: 1,
 });
 
 /**