Isle of Mull
I used Gimp 2.9.9 with the new HGT file import and the height maps from the NASA. You can read more about it here:
G'mics 3D elevation plugin:
Water texture from here:
The land colours are from a blurred screenshot from Google Earth.
Inkscape for the markers:
The sun is the standard "Sparks" brush from GIMP.
Cloud and bird brushes from https://www.deviantart.com
And a lot of fine tuning in GIMP, here is a screenshot of the layers dialogue: