The Default basemap is
OpenStreetMap PBF Vector Tiles with Terrain/Topo Style
user can change the style to other basemap stylesheets
or user can change to a raster image basemap from different providers * Internet required
https://geonamesmapexplorer.techmaven.net/feature/osm-vector-tiles
https://geonamesmapexplorer.techmaven.net/feature/online-layers-raster-tile-basemaps/
Offline area of interest downloads by default osm_vectortiles.mbtiles
you can optionally select contourlines_vectortiles.mbtiles and hillshade_rastertiles.mbtiles and satelliteimagery_rastertiles.mbtiles