Where did this software come from?
DrawMap is an example of the one of the strongest points for open source. Pretty much one person creates his idea of what a program should do. By offering the program as open source, other programmers can build on his start. The only rules of this game, are that the next programmer must also offer his version as open source as well, to be used by the next programmer.
What was in the original program
If the earth was a true sphere, the mapping from latitude and longitude to surface distance would be fairly simple, but the earth is a distorted sphere and the mapping is a set of increasingly complexe approximations. That mapping is the core of the original program.
What has been added
With separate layers, the contour data and hydrographic data are safely protected from changes in the user layer.
Using the program