Add other providers, max zoom per tile type

lib/models/tile_provider.dart

@@ -179,6 +179,46 @@ class DefaultTileProviders {
           ),
         ],
       ),
+      TileProvider(
+        id: 'usgs',
+        name: 'USGS',
+        tileTypes: [
+          TileType(
+            id: 'usgs_imagery_only',
+            name: 'Imagery Only',
+            urlTemplate: 'https://basemap.nationalmap.gov/arcgis/rest/services/USGSImageryOnly/MapServer/tile/{z}/{y}/{x}',
+            attribution: 'USGS The National Map',
+            maxZoom: 23,
+          ),
+          TileType(
+            id: 'usgs_imagery_topo',
+            name: 'Imagery Topo',
+            urlTemplate: 'https://basemap.nationalmap.gov/arcgis/rest/services/USGSImageryTopo/MapServer/tile/{z}/{y}/{x}',
+            attribution: 'USGS The National Map',
+            maxZoom: 23,
+          ),
+          TileType(
+            id: 'usgs_topo',
+            name: 'USGS Topo',
+            urlTemplate: 'https://basemap.nationalmap.gov/arcgis/rest/services/USGSTopo/MapServer/tile/{z}/{y}/{x}',
+            attribution: 'USGS The National Map',
+            maxZoom: 23,
+          ),
+        ],
+      ),
+      TileProvider(
+        id: 'opentopomap_memomaps',
+        name: 'OpenTopoMap/Memomaps',
+        tileTypes: [
+          TileType(
+            id: 'opentopomap_topo',
+            name: 'Topographic',
+            urlTemplate: 'https://tile.memomaps.de/tilegen/{z}/{y}/{x}.png',
+            attribution: 'Kartendaten: © OpenStreetMap-Mitwirkende, SRTM | Kartendarstellung: © OpenTopoMap (CC-BY-SA)',
+            maxZoom: 18,
+          ),
+        ],
+      ),
     ];
   }
 }