diff --git a/src/modules/geoportal/components/map-viewer.tsx b/src/modules/geoportal/components/map-viewer.tsx
index 42a5bcc..c13361d 100644
--- a/src/modules/geoportal/components/map-viewer.tsx
+++ b/src/modules/geoportal/components/map-viewer.tsx
@@ -362,6 +362,14 @@ export const MapViewer = forwardRef<MapViewerHandle, MapViewerProps>(
       map.on("load", () => {
         const m = resolvedMartinUrl;
 
+        // Hide OpenFreeMap's built-in boundary/admin layers (we have our own)
+        for (const layer of map.getStyle().layers) {
+          const id = layer.id.toLowerCase();
+          if (id.includes("boundar") || id.includes("admin") || (id.includes("border") && !id.includes("water"))) {
+            try { map.setLayoutProperty(layer.id, "visibility", "none"); } catch { /* noop */ }
+          }
+        }
+
         // === UAT z0-5: very coarse — lines only ===
         map.addSource(SOURCES.uatsZ0, { type: "vector", tiles: [`${m}/${SOURCES.uatsZ0}/{z}/{x}/{y}`], minzoom: 0, maxzoom: 5 });
         map.addLayer({ id: LAYER_IDS.uatsZ0Line, type: "line", source: SOURCES.uatsZ0, "source-layer": SOURCES.uatsZ0, maxzoom: 5,