You have to implement a image file with the name war3mapMap.blp to the map. Just create a new image and convert it to BLP. I don't know how big it should be, just check other images. You can extract them from a map.
Okay here's what i did, finished updating map, then saved, then attached everything. The minimap showed up but still had the start locations merc camps, etc. Then ingame the minimap was all blurry and screwed up, tell me what im doing wrong