diff --git a/assets/js/rover_map_hook.ts b/assets/js/rover_map_hook.ts
index cf928eb0..e87c8281 100644
--- a/assets/js/rover_map_hook.ts
+++ b/assets/js/rover_map_hook.ts
@@ -200,13 +200,15 @@ export const RoverMap: Partial<RoverMapHook> = {
       for (const c of cells) {
         this.cellLookup.set(cellKey(c.lat, c.lon), c)
       }
+      // Update radius before (re)drawing so the per-pixel clip uses the
+      // new value, otherwise the first paint can leak past the circle.
+      this.setDriveRadius(drive_radius_km)
       if (!this.qualityLayer) {
         this.qualityLayer = this.buildQualityLayer()
         this.qualityLayer.addTo(this.map)
       } else {
         this.qualityLayer.redraw()
       }
-      this.setDriveRadius(drive_radius_km)
     })
 
     this.handleEvent("focus_cell", (
@@ -338,27 +340,44 @@ export const RoverMap: Partial<RoverMapHook> = {
           }
         }
 
+        // Clip the heatmap to the drive-radius circle: pixels farther
+        // than driveRadiusKm from home stay transparent so the overlay
+        // never extends past the dashed circle.
+        const cosLat = Math.cos(self.homeLat * Math.PI / 180)
+        const kmPerPxX = lonPerPx * 111.0 * Math.max(cosLat, 0.1)
+        const kmPerPxY = latPerPx * 111.0
+        const homePxX = (self.homeLon - nw.lng) / lonPerPx
+        const homePxY = (nw.lat - self.homeLat) / latPerPx
+        const radiusKmSq = self.driveRadiusKm * self.driveRadiusKm
+
         const img = ctx.createImageData(w, h)
         const data = img.data
 
-        for (let i = 0; i < w * h; i++) {
-          let bestAlpha = 0
-          let bestRgb: [number, number, number] | null = null
+        for (let py = 0; py < h; py++) {
+          const dyKm = (py - homePxY) * kmPerPxY
+          for (let px = 0; px < w; px++) {
+            const dxKm = (px - homePxX) * kmPerPxX
+            if (dxKm * dxKm + dyKm * dyKm > radiusKmSq) continue
 
-          for (const tierColor of TIER_ORDER) {
-            const a = tierBuffers[tierColor][i]
-            if (a > 0.05 && a > bestAlpha) {
-              bestAlpha = a
-              bestRgb = TIER_RGB[tierColor]
+            const i = py * w + px
+            let bestAlpha = 0
+            let bestRgb: [number, number, number] | null = null
+
+            for (const tierColor of TIER_ORDER) {
+              const a = tierBuffers[tierColor][i]
+              if (a > 0.05 && a > bestAlpha) {
+                bestAlpha = a
+                bestRgb = TIER_RGB[tierColor]
+              }
             }
-          }
 
-          if (bestRgb && bestAlpha > 0) {
-            const o = i * 4
-            data[o] = bestRgb[0]
-            data[o + 1] = bestRgb[1]
-            data[o + 2] = bestRgb[2]
-            data[o + 3] = Math.min(255, Math.round(bestAlpha * 0.35 * 255))
+            if (bestRgb && bestAlpha > 0) {
+              const o = i * 4
+              data[o] = bestRgb[0]
+              data[o + 1] = bestRgb[1]
+              data[o + 2] = bestRgb[2]
+              data[o + 3] = Math.min(255, Math.round(bestAlpha * 0.35 * 255))
+            }
           }
         }