Viking is a free/open source program to manage GPS data (inc GPX, FIT, TCX and KML files). You can import and plot tracks, routes and waypoints, show OpenStreetMaps (OSM), Bing Aerial and other maps, generate Mapnik maps, geotag images, make new tracks, routes and waypoints, see real-time GPS position, etc. It is written mostly in C with GTK
We have hit CTRL+SHIFT+M to choose a new map layer.
Here at top we need to press the arrow to see the rest of the choices,
while at the same time there is this large empty space at the bottom.