diff --git a/src/app/api/geoip/route.ts b/src/app/api/geoip/route.ts
new file mode 100644
index 0000000..9cfb381
--- /dev/null
+++ b/src/app/api/geoip/route.ts
@@ -0,0 +1,30 @@
+import { type NextRequest } from 'next/server'
+
+export async function GET(request: NextRequest): Promise<Response> {
+    const forwarded = request.headers.get('x-forwarded-for');
+    const clientIp = forwarded ? forwarded.split(',')[0].trim() : null;
+
+    if (!clientIp) {
+        return Response.json({ latitude: null, longitude: null });
+    }
+
+    // Try ip-api.com first (free, reliable for real user IPs)
+    try {
+        const res = await fetch(`http://ip-api.com/json/${clientIp}?fields=status,lat,lon`, { cache: 'no-store' });
+        const json = await res.json();
+        if (json.status === 'success' && typeof json.lat === 'number' && typeof json.lon === 'number') {
+            return Response.json({ latitude: json.lat, longitude: json.lon });
+        }
+    } catch {}
+
+    // Fall back to ipwho.is
+    try {
+        const res = await fetch(`https://ipwho.is/${clientIp}`, { cache: 'no-store' });
+        const json = await res.json();
+        if (json.success && typeof json.latitude === 'number' && typeof json.longitude === 'number') {
+            return Response.json({ latitude: json.latitude, longitude: json.longitude });
+        }
+    } catch {}
+
+    return Response.json({ latitude: null, longitude: null });
+}
diff --git a/src/components/map/mapPageContent.tsx b/src/components/map/mapPageContent.tsx
index 028ba0b..572cdd2 100644
--- a/src/components/map/mapPageContent.tsx
+++ b/src/components/map/mapPageContent.tsx
@@ -16,6 +16,7 @@ import { CITY_DATA } from '@/data/citydata';
 import { CityDataProps, DataRangeKeys, ViewState } from '@/data/interfaces';
 import { calculateLayerRanges } from '@/components/utils/layerUtils';
 import { localStorageHelpers, loadInitialState } from '@/components/utils/localStorageUtils';
+import { useIpCityDefault } from '@/components/utils/useIpCityDefault';
 import { useMapTourLogic } from '@/components/utils/mapTourUtils';
 import { LAYER_CONSTANTS, NUM_LAYERS_OPTIONS } from '@/components/utils/pageConstants';
 import type { NumLayersMode } from '@/components/utils/pageConstants';
@@ -301,6 +302,13 @@ export default function MapPageContent(): JSX.Element {
         transitionInterpolator: new FlyToInterpolator()
     }), []);
 
+    useIpCityDefault((detectedIdx) => {
+        setIdx(detectedIdx);
+        setViewState(createViewStateForCity(detectedIdx));
+        const theseLayers = Object.keys(CITY_DATA.citiesArray[detectedIdx].dataRanges);
+        setCityLayers(theseLayers);
+    });
+
     const handleIdxChange = useCallback((idx: number) => {
         setIdx(idx);
         setViewState(createViewStateForCity(idx));
diff --git a/src/components/summarise/summarisePage.test.tsx b/src/components/summarise/summarisePage.test.tsx
index 500518b..2d6bf01 100644
--- a/src/components/summarise/summarisePage.test.tsx
+++ b/src/components/summarise/summarisePage.test.tsx
@@ -18,6 +18,7 @@ vi.mock('@/components/utils/localStorageUtils', () => ({
     getItem: vi.fn(() => null),
     setItem: vi.fn(),
   },
+  fetchIpDefaultCityIdx: vi.fn(() => Promise.resolve(0)),
 }))
 
 describe('SummarisePage', () => {
diff --git a/src/components/summarise/summarisePageContent.tsx b/src/components/summarise/summarisePageContent.tsx
index cfb565e..c291ed8 100644
--- a/src/components/summarise/summarisePageContent.tsx
+++ b/src/components/summarise/summarisePageContent.tsx
@@ -7,6 +7,7 @@ import Control from '@/components/summarise/control';
 import styles from '@/styles/summarise.module.css';
 import Content from '@/components/summarise/citySummaryData';
 import { localStorageHelpers } from '@/components/utils/localStorageUtils';
+import { useIpCityDefault } from '@/components/utils/useIpCityDefault';
 
 export default function SummarisePageContent(): JSX.Element {
 
@@ -28,6 +29,8 @@ export default function SummarisePageContent(): JSX.Element {
     const hasFullQuery = urlData.hasFullQuery;
     const [idx, setIdx] = useState(urlData.idx);
 
+    useIpCityDefault(setIdx);
+
     useEffect(() => {
         if (hasFullQuery) return;
         const cityName = contentArray[idx]?.name ?? '';
diff --git a/src/components/transform/transformPage.test.tsx b/src/components/transform/transformPage.test.tsx
index 539c29c..278d7e8 100644
--- a/src/components/transform/transformPage.test.tsx
+++ b/src/components/transform/transformPage.test.tsx
@@ -7,7 +7,8 @@ vi.mock('@/components/utils/localStorageUtils', () => ({
     getItem: vi.fn(() => null),
     setItem: vi.fn(),
     removeItem: vi.fn()
-  }
+  },
+  fetchIpDefaultCityIdx: vi.fn(() => Promise.resolve(0)),
 }))
 
 vi.mock('@/components/utils/transformTourUtils', () => ({
diff --git a/src/components/transform/transformPage.tsx b/src/components/transform/transformPage.tsx
index 44cebec..f97ad67 100644
--- a/src/components/transform/transformPage.tsx
+++ b/src/components/transform/transformPage.tsx
@@ -16,6 +16,7 @@ import { CityDataProps } from "@/data/interfaces";
 import { CITY_DATA } from '@/data/citydata';
 import { DataRangeKeys, ViewState } from '@/data/interfaces';
 import { localStorageHelpers } from '@/components/utils/localStorageUtils';
+import { useIpCityDefault } from '@/components/utils/useIpCityDefault';
 import { useTransformTourLogic } from '@/components/utils/transformTourUtils';
 import { LAYER_CONSTANTS, OUTPUT_LAYER_TYPES } from '@/components/utils/pageConstants';
 import type { OutputLayerType } from '@/components/utils/pageConstants';
@@ -282,6 +283,11 @@ export default function TransformPage(): JSX.Element {
         transitionInterpolator: new FlyToInterpolator()
     }), []);
 
+    useIpCityDefault((detectedIdx) => {
+        setIdx(detectedIdx);
+        setViewState(createViewStateForCity(detectedIdx));
+    });
+
     const citiesData = useMemo(() => ({
         citiesArray: CITY_DATA.citiesArray,
         citiesCount: CITY_DATA.citiesArray.length,
diff --git a/src/components/utils/localStorageUtils.tsx b/src/components/utils/localStorageUtils.tsx
index a10cc73..558cb1f 100644
--- a/src/components/utils/localStorageUtils.tsx
+++ b/src/components/utils/localStorageUtils.tsx
@@ -1,5 +1,13 @@
 import { useState, useReducer } from 'react';
 import { DataRangeKeys } from '@/data/interfaces';
+import { findNearestCityIdx } from '@/data/citydata';
+
+export async function fetchIpDefaultCityIdx(): Promise<number> {
+    const res = await fetch('/api/geoip');
+    const json = await res.json();
+    if (typeof json.latitude !== 'number' || typeof json.longitude !== 'number') return 0;
+    return findNearestCityIdx(json.latitude as number, json.longitude as number);
+}
 
 export const localStorageHelpers = {
 
diff --git a/src/components/utils/useIpCityDefault.tsx b/src/components/utils/useIpCityDefault.tsx
new file mode 100644
index 0000000..1f6750a
--- /dev/null
+++ b/src/components/utils/useIpCityDefault.tsx
@@ -0,0 +1,23 @@
+"use client"
+
+import { useEffect, useRef } from 'react';
+import { localStorageHelpers, fetchIpDefaultCityIdx } from './localStorageUtils';
+
+export function useIpCityDefault(onResolve: (idx: number) => void): void {
+    const callbackRef = useRef(onResolve);
+    useEffect(() => { callbackRef.current = onResolve; });
+
+    useEffect(() => {
+        // '0' means either "never detected" or "failed detection" — treat both as unset
+        const stored = localStorageHelpers.getItem('uaCityIdx');
+        if (stored !== null && stored !== '0') return;
+        fetchIpDefaultCityIdx()
+            .then(idx => {
+                if (idx > 0) {
+                    localStorageHelpers.setItem('uaCityIdx', idx.toString());
+                    callbackRef.current(idx);
+                }
+            })
+            .catch(() => {});
+    }, []);  
+}
diff --git a/src/data/citydata.tsx b/src/data/citydata.tsx
index 112c002..e824cfe 100644
--- a/src/data/citydata.tsx
+++ b/src/data/citydata.tsx
@@ -1478,3 +1478,14 @@ const washington = {
 export const CITY_DATA = {
     "citiesArray": [berlin, hamburg, london, mannheim, muenster, paris, philadelphia, utrecht, washington],
 };
+
+export function findNearestCityIdx(lat: number, lon: number): number {
+    return CITY_DATA.citiesArray.reduce((bestIdx, city, i) => {
+        const dLat = city.initialViewState.latitude - lat;
+        const dLon = city.initialViewState.longitude - lon;
+        const best = CITY_DATA.citiesArray[bestIdx].initialViewState;
+        const bLat = best.latitude - lat;
+        const bLon = best.longitude - lon;
+        return (dLat * dLat + dLon * dLon) < (bLat * bLat + bLon * bLon) ? i : bestIdx;
+    }, 0);
+}