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
Perhaps allow
viking --tool panviking --tool selectetc. to control initial mode from command line.Else panning the screen with one's finger might drag points around, when we were just intending to look at the map, not edit it.
In fact there could also be a --read-only, meaning all files are not allowed to be edited.