Why do maps sometimes switch to satellite and roads?

Problem: You have chosen a map source type like Terrain or Hiking Maps but when you zoom in or out the maps automatically switch to another theme or obviously the "wrong" map type is being displayed.
Background: Not all map sources are available at all resolutions and in all areas of the world. So if the resolutions range of geographical coverage for a map source is exceeded, TrailRunner will display the best logical match it can find. For high resolutions this is satellite and for low resolutions this is roads.
Note: TrailRunner displays a small warning at the bottom of the main window to inform you about the adaptive source change.