This game is amazing.
Unfortunately, it is too complex and difficult to create and import a real world map into the game. I hope the developers put some energy into making this process easier and more fun.
The attachments are an attempt at following the instructions here:
The game doesn't recognize them. It is as though they do not exist. I expect that they won't work too, but maybe somebody can get them to work.
They are in a folder in
\steamapps\common\Transport Fever 2\maps
I tried to find the correct folder by looking for other maps but couldn't find any!