Maybe like this: https://youtu.be/fmwhf0i84g4 duration 4 minutes.
There is a very long tutorial about making game maps, fortunately the basics have been scripted. Attached, unzip put render-map-2-no-snow.py in your Gimp User plugins folder. ( I have just seen you are using Gimp 2.8) C:\Users\"yourname"\.gimp-2.8\plug-ins
The video is Gimp 2.10, it is the same for Gimp 2.8
The main thing is the starting layer names. They are fixed in the script. Base layer Land Start layer above Mountains Start
...not what you want.. Looking at google maps, these are very plain you could probably take one and clone out place etc. Satellite view is better, although same thing, clone out names.
There is a very long tutorial about making game maps, fortunately the basics have been scripted. Attached, unzip put render-map-2-no-snow.py in your Gimp User plugins folder. ( I have just seen you are using Gimp 2.8) C:\Users\"yourname"\.gimp-2.8\plug-ins
The video is Gimp 2.10, it is the same for Gimp 2.8
The main thing is the starting layer names. They are fixed in the script. Base layer Land Start layer above Mountains Start
...not what you want.. Looking at google maps, these are very plain you could probably take one and clone out place etc. Satellite view is better, although same thing, clone out names.