One of the things that strikes me about using someone else's map is that usually we would want to adapt it in some way or add to it. To be able to do that depends on the format it is in and the software that we have available and whether the images in the map are accessible and changeable within the file format and/or are available separately. Some maps look very good, but I know I will never use them because I don't have, and can't access, the means to adapt them.