⚡️ use TopoJSON for NUTS3 everywhere

src/app.config.ts

@@ -1,7 +1,7 @@
 import {Fill, Stroke, Style} from 'ol/style';
-import {GeoJSON} from 'ol/format';
 import {OSM, Vector as VectorSource} from 'ol/source';
 import {Tile, Vector as VectorLayer} from 'ol/layer';
+import {TopoJSON} from 'ol/format';
 import {View} from 'ol';
 
 import env from './env.config.json';
@@ -85,8 +85,8 @@ export const nuts2Layer = new VectorLayer({
 
 export const nuts3IndexSource = new VectorSource({
   //features: new GeoJSON().readFeatures(nuts3),
-  format: new GeoJSON(),
-  url: require('./data/NUTS_RG_20M_2016_3857_LEVL_3.geojson').default,
+  format: new TopoJSON(),
+  url: require('./data/NUTS_RG_20M_2016_3857_LEVL_3.topojson').default,
   overlaps: false,
 });