How could I convert this image into a Gimp map

[Hai-Etlik]

Note that Google maps has copyright notices down in the corner for a reason. There is some grey area due to copyright (supposedly) not applying to simple facts, and where things are is a matter of fact rather than expression, but copying existing maps without license is a bad idea. Map companies often include minor intentional errors for instance to make it subject to copyright. Also everything about the map that IS expression rather than just facts is subject to copyright. Also there may be 'database rights' which is an ability to restrict particular collections of facts in a similar manner to copyright which may be a problem.

In short, although I'm not a lawyer and can't say for sure that copying over Google Maps is going to get you in trouble, there's a good chance it's a bad idea and it might be a better to use some other source like Natural Earth, OpenStreetMap, or USGS.

Also this sub-forum is for providing worked out tutorials. Asking questions belongs in How Do I ???