feat: implement hotspot visualization on map

- Add HotspotSeverity type and HotspotWithSeverity interface
- Implement getHotspots() method in analyticsService with severity calculation
- Add hotspot layer to MapView component with color-coded circles
- Create hotspot markers with severity icons and report count badges
- Add detailed hotspot popups showing report count, severity score, radius, and dates
- Implement hotspot toggle control in MapFilters with loading state
- Add hotspot severity legend to MapFilters
- Integrate hotspot data fetching in MapPage with sample fallback data
- Color-code hotspot boundaries: yellow (low), orange (medium/high), red (critical)
- Display hotspot statistics in interactive popups

Implements task 12: Create hotspot visualization
Requirements: 3.2, 3.3, 3.5

src/components/map/MapFilters.tsx

@@ -8,6 +8,9 @@ interface MapFiltersProps {
   showClusters: boolean;
   onToggleHeatmap: () => void;
   showHeatmap: boolean;
+  onToggleHotspots?: () => void;
+  showHotspots?: boolean;
+  isLoadingHotspots?: boolean;
 }
 
 export function MapFilters({
@@ -17,6 +20,9 @@ export function MapFilters({
   showClusters,
   onToggleHeatmap,
   showHeatmap,
+  onToggleHotspots,
+  showHotspots = false,
+  isLoadingHotspots = false,
 }: MapFiltersProps) {
   const [isExpanded, setIsExpanded] = useState(false);
 
@@ -153,6 +159,62 @@ export function MapFilters({
             </button>
           </div>
 
+          {/* Hotspots Toggle */}
+          {onToggleHotspots && (
+            <div className="flex items-center justify-between">
+              <label htmlFor="hotspots-toggle" className="text-sm font-medium text-gray-700 flex items-center gap-2">
+                Hotspots
+                {isLoadingHotspots && (
+                  <svg className="animate-spin h-4 w-4 text-blue-600" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24">
+                    <circle className="opacity-25" cx="12" cy="12" r="10" stroke="currentColor" strokeWidth="4"></circle>
+                    <path className="opacity-75" fill="currentColor" d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4zm2 5.291A7.962 7.962 0 014 12H0c0 3.042 1.135 5.824 3 7.938l3-2.647z"></path>
+                  </svg>
+                )}
+              </label>
+              <button
+                id="hotspots-toggle"
+                onClick={onToggleHotspots}
+                disabled={isLoadingHotspots}
+                className={`relative inline-flex h-6 w-11 items-center rounded-full transition-colors ${
+                  showHotspots ? 'bg-orange-600' : 'bg-gray-200'
+                } ${isLoadingHotspots ? 'opacity-50 cursor-not-allowed' : ''}`}
+                role="switch"
+                aria-checked={showHotspots}
+              >
+                <span
+                  className={`inline-block h-4 w-4 transform rounded-full bg-white transition-transform ${
+                    showHotspots ? 'translate-x-6' : 'translate-x-1'
+                  }`}
+                />
+              </button>
+            </div>
+          )}
+
+          {/* Hotspot Legend */}
+          {showHotspots && onToggleHotspots && (
+            <div className="pt-2 border-t border-gray-200">
+              <p className="text-xs font-medium text-gray-700 mb-2">Hotspot Severity</p>
+              <div className="space-y-1">
+                <div className="flex items-center gap-2 text-xs">
+                  <div className="w-3 h-3 rounded-full bg-yellow-300 border border-yellow-400"></div>
+                  <span className="text-gray-600">Low (5-9 reports)</span>
+                </div>
+                <div className="flex items-center gap-2 text-xs">
+                  <div className="w-3 h-3 rounded-full bg-orange-400 border border-orange-500"></div>
+                  <span className="text-gray-600">Medium (10-14 reports)</span>
+                </div>
+                <div className="flex items-center gap-2 text-xs">
+                  <div className="w-3 h-3 rounded-full bg-orange-500 border border-orange-600"></div>
+                  <span className="text-gray-600">High (15-19 reports)</span>
+                </div>
+                <div className="flex items-center gap-2 text-xs">
+                  <div className="w-3 h-3 rounded-full bg-red-600 border border-red-700"></div>
+                  <span className="text-gray-600">Critical (20+ reports)</span>
+                </div>
+              </div>
+            </div>
+          )}
+
           {/* Date Range */}
           <div>
             <label className="block text-sm font-medium text-gray-700 mb-2">

src/components/map/MapView.tsx

@@ -5,7 +5,7 @@ import 'leaflet.markercluster/dist/MarkerCluster.css';
 import 'leaflet.markercluster/dist/MarkerCluster.Default.css';
 import 'leaflet.markercluster';
 import 'leaflet.heat';
-import type { Report, CleanupEvent, FilterState } from '@/types';
+import type { Report, CleanupEvent, FilterState, HotspotWithSeverity } from '@/types';
 
 // Fix for default marker icons in Leaflet with Vite
 import markerIcon2x from 'leaflet/dist/images/marker-icon-2x.png';
@@ -22,11 +22,13 @@ L.Icon.Default.mergeOptions({
 interface MapViewProps {
   reports: Report[];
   events?: CleanupEvent[];
+  hotspots?: HotspotWithSeverity[];
   filters?: FilterState;
   onMarkerClick?: (reportId: string) => void;
   onMapClick?: (lat: number, lng: number) => void;
   showHeatmap?: boolean;
   showClusters?: boolean;
+  showHotspots?: boolean;
   center?: [number, number];
   zoom?: number;
 }
@@ -34,11 +36,13 @@ interface MapViewProps {
 export function MapView({
   reports,
   events = [],
+  hotspots = [],
   filters,
   onMarkerClick,
   onMapClick,
   showClusters = true,
   showHeatmap = false,
+  showHotspots = false,
   center = [53.3498, -6.2603], // Dublin, Ireland default
   zoom = 7,
 }: MapViewProps) {
@@ -47,6 +51,7 @@ export function MapView({
   const markersLayerRef = useRef<L.LayerGroup | null>(null);
   const clusterGroupRef = useRef<L.MarkerClusterGroup | null>(null);
   const heatLayerRef = useRef<L.HeatLayer | null>(null);
+  const hotspotsLayerRef = useRef<L.LayerGroup | null>(null);
 
   // Initialize map
   useEffect(() => {
@@ -71,6 +76,9 @@ export function MapView({
     // Create markers layer
     markersLayerRef.current = L.layerGroup();
 
+    // Create hotspots layer
+    hotspotsLayerRef.current = L.layerGroup();
+
     // Create cluster group with custom configuration
     clusterGroupRef.current = L.markerClusterGroup({
       maxClusterRadius: 50, // Cluster markers within 50 pixels
@@ -103,6 +111,7 @@ export function MapView({
       markersLayerRef.current = null;
       clusterGroupRef.current = null;
       heatLayerRef.current = null;
+      hotspotsLayerRef.current = null;
     };
   }, []);
 
@@ -276,6 +285,87 @@ export function MapView({
     }
   }, [reports, filters, showHeatmap]);
 
+  // Update hotspots when hotspots data or showHotspots changes
+  useEffect(() => {
+    if (!mapInstanceRef.current || !hotspotsLayerRef.current) return;
+
+    const map = mapInstanceRef.current;
+    const hotspotsLayer = hotspotsLayerRef.current;
+
+    // Remove existing hotspots layer if it exists
+    if (map.hasLayer(hotspotsLayer)) {
+      map.removeLayer(hotspotsLayer);
+    }
+
+    // Clear existing hotspots
+    hotspotsLayer.clearLayers();
+
+    // Only create hotspot layer if showHotspots is true
+    if (showHotspots && hotspots.length > 0) {
+      hotspots.forEach((hotspot) => {
+        // Get color based on severity
+        const { color, fillColor, opacity } = getHotspotStyle(hotspot.severity);
+
+        // Create circle for hotspot boundary
+        const circle = L.circle([hotspot.latitude, hotspot.longitude], {
+          radius: hotspot.radius,
+          color: color,
+          fillColor: fillColor,
+          fillOpacity: opacity,
+          weight: 2,
+        });
+
+        // Create popup with hotspot details
+        const lastReportDate = new Date(hotspot.lastReportDate).toLocaleDateString();
+        const calculatedDate = new Date(hotspot.calculatedAt).toLocaleDateString();
+        
+        circle.bindPopup(`
+          <div class="p-3 min-w-[200px]">
+            <h3 class="font-bold text-base mb-2 flex items-center gap-2">
+              <span class="text-2xl">${getHotspotIcon(hotspot.severity)}</span>
+              <span>${getSeverityLabel(hotspot.severity)} Hotspot</span>
+            </h3>
+            <div class="space-y-1 text-sm">
+              <p class="flex justify-between">
+                <span class="text-gray-600">Reports:</span>
+                <span class="font-semibold">${hotspot.reportCount}</span>
+              </p>
+              <p class="flex justify-between">
+                <span class="text-gray-600">Severity Score:</span>
+                <span class="font-semibold">${hotspot.severityScore.toFixed(2)}</span>
+              </p>
+              <p class="flex justify-between">
+                <span class="text-gray-600">Radius:</span>
+                <span class="font-semibold">${hotspot.radius}m</span>
+              </p>
+              <p class="flex justify-between">
+                <span class="text-gray-600">Last Report:</span>
+                <span class="font-semibold">${lastReportDate}</span>
+              </p>
+              <p class="text-xs text-gray-500 mt-2 pt-2 border-t">
+                Calculated: ${calculatedDate}
+              </p>
+            </div>
+          </div>
+        `);
+
+        // Add center marker for hotspot
+        const centerMarker = L.marker([hotspot.latitude, hotspot.longitude], {
+          icon: createHotspotMarkerIcon(hotspot.severity, hotspot.reportCount),
+        });
+
+        centerMarker.bindPopup(circle.getPopup()!);
+
+        // Add to layer
+        hotspotsLayer.addLayer(circle);
+        hotspotsLayer.addLayer(centerMarker);
+      });
+
+      // Add hotspots layer to map
+      hotspotsLayer.addTo(map);
+    }
+  }, [hotspots, showHotspots]);
+
   // Handle geolocation
   const handleGeolocation = () => {
     if (!navigator.geolocation) {
@@ -457,3 +547,111 @@ function getLitterTypeLabel(litterType: string): string {
   const label = litterType.charAt(0).toUpperCase() + litterType.slice(1);
   return label;
 }
+
+// Helper function to get hotspot style based on severity
+function getHotspotStyle(severity: string): { color: string; fillColor: string; opacity: number } {
+  const styles = {
+    low: {
+      color: '#FCD34D', // yellow-300
+      fillColor: '#FEF3C7', // yellow-100
+      opacity: 0.3,
+    },
+    medium: {
+      color: '#FB923C', // orange-400
+      fillColor: '#FFEDD5', // orange-100
+      opacity: 0.4,
+    },
+    high: {
+      color: '#F97316', // orange-500
+      fillColor: '#FED7AA', // orange-200
+      opacity: 0.5,
+    },
+    critical: {
+      color: '#DC2626', // red-600
+      fillColor: '#FEE2E2', // red-100
+      opacity: 0.6,
+    },
+  };
+
+  return styles[severity as keyof typeof styles] || styles.low;
+}
+
+// Helper function to create hotspot marker icon
+function createHotspotMarkerIcon(severity: string, reportCount: number): L.DivIcon {
+  const colors = {
+    low: '#FCD34D',
+    medium: '#FB923C',
+    high: '#F97316',
+    critical: '#DC2626',
+  };
+
+  const color = colors[severity as keyof typeof colors] || colors.low;
+  const icon = getHotspotIcon(severity);
+
+  return L.divIcon({
+    className: 'hotspot-marker',
+    html: `
+      <div style="
+        width: 40px;
+        height: 40px;
+        background-color: ${color};
+        border: 3px solid white;
+        border-radius: 50%;
+        box-shadow: 0 3px 6px rgba(0,0,0,0.4);
+        display: flex;
+        align-items: center;
+        justify-content: center;
+        color: white;
+        font-size: 20px;
+        font-weight: bold;
+        position: relative;
+      ">
+        ${icon}
+        <div style="
+          position: absolute;
+          bottom: -8px;
+          right: -8px;
+          background-color: white;
+          color: ${color};
+          border: 2px solid ${color};
+          border-radius: 50%;
+          width: 24px;
+          height: 24px;
+          display: flex;
+          align-items: center;
+          justify-content: center;
+          font-size: 11px;
+          font-weight: bold;
+          box-shadow: 0 2px 4px rgba(0,0,0,0.2);
+        ">
+          ${reportCount}
+        </div>
+      </div>
+    `,
+    iconSize: [40, 40],
+    iconAnchor: [20, 20],
+  });
+}
+
+// Helper function to get hotspot icon based on severity
+function getHotspotIcon(severity: string): string {
+  const icons: Record<string, string> = {
+    low: '⚠️',
+    medium: '🔶',
+    high: '🔥',
+    critical: '🚨',
+  };
+  const icon = icons[severity];
+  return icon !== undefined ? icon : '⚠️';
+}
+
+// Helper function to get severity label
+function getSeverityLabel(severity: string): string {
+  const labels: Record<string, string> = {
+    low: 'Low',
+    medium: 'Medium',
+    high: 'High',
+    critical: 'Critical',
+  };
+  return labels[severity] || 'Unknown';
+}

src/pages/MapPage.tsx

@@ -1,6 +1,7 @@
-import { useState } from 'react';
+import { useState, useEffect } from 'react';
 import { MapView, MapFilters } from '@/components/map';
-import type { Report, FilterState } from '@/types';
+import { analyticsService } from '@/services/analyticsService';
+import type { Report, FilterState, HotspotWithSeverity } from '@/types';
 
 /**
  * Map page - Interactive map displaying litter reports and cleanup events
@@ -10,6 +11,9 @@ export function MapPage() {
   const [filters, setFilters] = useState<FilterState>({});
   const [showClusters, setShowClusters] = useState(true);
   const [showHeatmap, setShowHeatmap] = useState(false);
+  const [showHotspots, setShowHotspots] = useState(false);
+  const [hotspots, setHotspots] = useState<HotspotWithSeverity[]>([]);
+  const [isLoadingHotspots, setIsLoadingHotspots] = useState(false);
 
   // Sample data for demonstration (will be replaced with API data in later tasks)
   const sampleReports: Report[] = [
@@ -124,6 +128,63 @@ export function MapPage() {
     setShowHeatmap(!showHeatmap);
   };
 
+  const handleToggleHotspots = () => {
+    setShowHotspots(!showHotspots);
+  };
+
+  // Fetch hotspots when hotspot view is enabled
+  useEffect(() => {
+    if (showHotspots && hotspots.length === 0) {
+      setIsLoadingHotspots(true);
+      analyticsService.getHotspots()
+        .then((data) => {
+          setHotspots(data);
+        })
+        .catch((error) => {
+          console.error('Failed to fetch hotspots:', error);
+          // Use sample hotspot data for demonstration
+          setHotspots([
+            {
+              id: 'hotspot1',
+              latitude: 53.3498,
+              longitude: -6.2603,
+              radius: 500,
+              reportCount: 15,
+              severityScore: 0.75,
+              lastReportDate: new Date('2024-01-20'),
+              calculatedAt: new Date('2024-01-21'),
+              severity: 'high',
+            },
+            {
+              id: 'hotspot2',
+              latitude: 51.8969,
+              longitude: -8.4863,
+              radius: 450,
+              reportCount: 8,
+              severityScore: 0.45,
+              lastReportDate: new Date('2024-01-19'),
+              calculatedAt: new Date('2024-01-21'),
+              severity: 'medium',
+            },
+            {
+              id: 'hotspot3',
+              latitude: 53.2707,
+              longitude: -9.0568,
+              radius: 600,
+              reportCount: 22,
+              severityScore: 0.88,
+              lastReportDate: new Date('2024-01-21'),
+              calculatedAt: new Date('2024-01-21'),
+              severity: 'critical',
+            },
+          ]);
+        })
+        .finally(() => {
+          setIsLoadingHotspots(false);
+        });
+    }
+  }, [showHotspots]);
+
   return (
     <div className="h-screen flex flex-col">
       <div className="bg-white border-b border-gray-200 px-4 py-4 sm:px-6 lg:px-8">
@@ -137,9 +198,11 @@ export function MapPage() {
         <div className="h-full bg-white rounded-lg shadow-lg overflow-hidden relative">
           <MapView
             reports={sampleReports}
+            hotspots={hotspots}
             filters={filters}
             showClusters={showClusters}
             showHeatmap={showHeatmap}
+            showHotspots={showHotspots}
             onMarkerClick={handleMarkerClick}
             onMapClick={handleMapClick}
           />
@@ -151,6 +214,9 @@ export function MapPage() {
             showClusters={showClusters}
             onToggleHeatmap={handleToggleHeatmap}
             showHeatmap={showHeatmap}
+            onToggleHotspots={handleToggleHotspots}
+            showHotspots={showHotspots}
+            isLoadingHotspots={isLoadingHotspots}
           />
         </div>
       </div>

src/services/analyticsService.ts

@@ -1,6 +1,6 @@
 // Analytics service for API interactions
 import { apiClient } from './api';
-import type { AnalyticsSummary, TimeSeriesDataPoint, LitterTypeDistribution, QuantityAggregation } from '@/types';
+import type { AnalyticsSummary, TimeSeriesDataPoint, LitterTypeDistribution, QuantityAggregation, Hotspot, HotspotWithSeverity, HotspotSeverity } from '@/types';
 
 class AnalyticsService {
   /**
@@ -91,6 +91,39 @@ class AnalyticsService {
 
     return response.blob();
   }
+
+  /**
+   * Get hotspot data for map visualization
+   */
+  async getHotspots(): Promise<HotspotWithSeverity[]> {
+    const hotspots = await apiClient.get<Hotspot[]>('/analytics/hotspots');
+    
+    // Calculate severity based on score and add to each hotspot
+    return hotspots.map(hotspot => ({
+      ...hotspot,
+      severity: this.calculateHotspotSeverity(hotspot.severityScore, hotspot.reportCount),
+    }));
+  }
+
+  /**
+   * Calculate hotspot severity based on score and report count
+   */
+  private calculateHotspotSeverity(score: number, reportCount: number): HotspotSeverity {
+    // Critical: score >= 0.8 or 20+ reports
+    if (score >= 0.8 || reportCount >= 20) {
+      return 'critical';
+    }
+    // High: score >= 0.6 or 15+ reports
+    if (score >= 0.6 || reportCount >= 15) {
+      return 'high';
+    }
+    // Medium: score >= 0.4 or 10+ reports
+    if (score >= 0.4 || reportCount >= 10) {
+      return 'medium';
+    }
+    // Low: everything else
+    return 'low';
+  }
 }
 
 export const analyticsService = new AnalyticsService();

src/types/index.ts

@@ -83,6 +83,12 @@ export interface Hotspot {
   calculatedAt: Date;
 }
 
+export type HotspotSeverity = 'low' | 'medium' | 'high' | 'critical';
+
+export interface HotspotWithSeverity extends Hotspot {
+  severity: HotspotSeverity;
+}
+
 // DTOs (Data Transfer Objects)
 export interface CreateReportDTO {
   photos: File[];