Nice to see a neighbor here writing. Please, answer a little query and think we will have an answer:
1. What kind of map do you want to create? A marine one?
2. With which garmin unit you are going to use it?
3. What is the perpose of this map?
4. Do you have data of Danube or you are collecting one?
Mapsource is a tool for using garmin maps but not for creating ones. The software which is creating some of the garmin maps, and gladly is available in the free society "internet", is called MPC or Mapsource Product Creator. Have a look:
[Only registered and activated users can see links. ]