short answer
At the simplest level, making a map like that only requires one piece of info. The game uses ONE pure-white pixel (single dot) to mark a province. Meaning where the flag shows up on the maps. If you use your paint program to put those dots in then you can use the map editor in the game and have it guess at all the neighbor connections.
longer answer
Using map editor..
Of course, drawing border lines help it to make more logical decisions about neighbors. It likes red borders for this which can be hard on the eyes. But you can use red borders while you are working the map and then change it to something more subtle before you release it for play.
Setting terrains is usually desired so that everyone isnt playing just on "plains". And the game wont crash by trying to assign a water nation to the game.
Having it assign randomly chosen names to the map will hep since it makes it easy to go thru and manually change them to match the real area you are duplicating.
Outside of the map editor....
Setting specific start locations involves manually editing the .map file in something like notepad or wordpad. There is a full PDF on the map commands in your Dom3 doc directory. Here is a link to a quickie list.
http://www.dom3minions.com/docs/map_qref.txt