diff --git a/frontend/src/App.tsx b/frontend/src/App.tsx
index e5d88b15..27bc2235 100644
--- a/frontend/src/App.tsx
+++ b/frontend/src/App.tsx
@@ -305,6 +305,8 @@ function WorkbenchApp({ username, accessMode, loggingOut, onLogout }: WorkbenchA
     selectedProjectId,
     availableVectorDatasets,
     loadDatasetJobs,
+    // Bind the comparison to whatever the operator has selected on the map.
+    getSelection: () => ({ bbox: mapSelectionBbox ?? null, areaId: selectedMapAreaId ?? null }),
   })
   const {
     qaCandidateDatasetId,
diff --git a/frontend/src/components/analysis/ChangeDetectionPanel.tsx b/frontend/src/components/analysis/ChangeDetectionPanel.tsx
index 276ba9e5..b057c41d 100644
--- a/frontend/src/components/analysis/ChangeDetectionPanel.tsx
+++ b/frontend/src/components/analysis/ChangeDetectionPanel.tsx
@@ -120,6 +120,10 @@ export function ChangeDetectionPanel({
               <span className="metric">{result.removed_count}</span>
               <span>Verdwenen</span>
             </div>
+            <div>
+              <span className="metric">{result.modified_count ?? 0}</span>
+              <span>Gewijzigd</span>
+            </div>
             <div>
               <span className="metric">{result.unchanged_count}</span>
               <span>Ongewijzigd</span>
diff --git a/frontend/src/hooks/useChangeDetectionWorkflow.ts b/frontend/src/hooks/useChangeDetectionWorkflow.ts
index 9f41fcf2..7d1749eb 100644
--- a/frontend/src/hooks/useChangeDetectionWorkflow.ts
+++ b/frontend/src/hooks/useChangeDetectionWorkflow.ts
@@ -1,18 +1,29 @@
 import { useState } from 'react'
 import { analysisApi } from '../services/api'
-import type { ChangeDetectionSummary, DatasetCreateResponse } from '../types'
+import type { ChangeDetectionSummary, DatasetCreateResponse, VectorSelectionBBox } from '../types'
 import { formatError } from '../lib/formatError'
 
 interface ChangeDetectionWorkflowOptions {
   selectedProjectId: string | null
   availableVectorDatasets: DatasetCreateResponse[]
   loadDatasetJobs: (projectId: string, datasetId: string) => Promise<void>
+  /**
+   * Reads the active map selection when the comparison is started. Without a
+   * selection the comparison covers both datasets entire, which is rarely the
+   * question being asked and returns a payload no map can draw.
+   *
+   * A getter rather than a value because this hook runs before the selection
+   * state is declared in the component; it is only ever called from a user
+   * event, long after that binding is initialised.
+   */
+  getSelection?: () => { bbox: VectorSelectionBBox | null; areaId: string | null }
 }
 
 export function useChangeDetectionWorkflow({
   selectedProjectId,
   availableVectorDatasets,
   loadDatasetJobs,
+  getSelection,
 }: ChangeDetectionWorkflowOptions) {
   const [changeSourceDatasetId, setChangeSourceDatasetId] = useState('')
   const [changeTargetDatasetId, setChangeTargetDatasetId] = useState('')
@@ -41,12 +52,15 @@ export function useChangeDetectionWorkflow({
     setChangeDetectionError(null)
     setChangeDetectionResult(null)
     setRunningChangeDetection(true)
+    const selection = getSelection?.() ?? { bbox: null, areaId: null }
     try {
       const job = await analysisApi.runChangeDetection({
         source_dataset_id: sourceDatasetId,
         target_dataset_id: targetDatasetId,
         iou_threshold: changeIouThreshold,
         include_unchanged: changeIncludeUnchanged,
+        ...(selection.bbox ? { bbox: selection.bbox } : {}),
+        ...(selection.areaId ? { area_id: selection.areaId } : {}),
       })
       if (job.status !== 'success') {
         throw new Error(job.error_message || 'Change detection job failed')
diff --git a/frontend/src/types.ts b/frontend/src/types.ts
index 7293d7ca..05385524 100644
--- a/frontend/src/types.ts
+++ b/frontend/src/types.ts
@@ -1055,7 +1055,13 @@ export interface ChangeDetectionRequest {
   source_dataset_id: string
   target_dataset_id: string
   iou_threshold: number
+  /** Below this the footprints are separate objects rather than one redrawn. */
+  modified_threshold?: number
   include_unchanged: boolean
+  /** Without a selection the comparison covers both datasets in full. */
+  bbox?: VectorSelectionBBox | null
+  area_id?: string | null
+  preview_limit?: number
 }
 
 export interface ChangeDetectionSummary {
@@ -1065,8 +1071,15 @@ export interface ChangeDetectionSummary {
   target_feature_count: number
   added_count: number
   removed_count: number
+  /** A footprint that was redrawn, not demolished and rebuilt. */
+  modified_count?: number
   unchanged_count: number
   iou_threshold: number
+  modified_iou_threshold?: number | null
+  selection_area_id?: string | null
+  /** Counts cover the whole selection; the GeoJSON is capped. */
+  preview_limit?: number | null
+  preview_truncated?: boolean
   warnings: string[]
   generated_at: string
   geojson: GeoJSON.FeatureCollection