For maps, it's always best to use powers of 2 for map dimensions, because of the way memory addressing is done (I think that's how you say it). Basically, if you make it 512 by 512, then your computer will allocate enough memory space to accomodate a 512 by 512 image. But if you make it 513 by 513, then it'll treat it as if it was 1024 by 1024, preventing that much extra texture space in your video card's RAM, from being used for other textures. Its for efficiency. If you remember Lightspeed & co.'s hi-res fighter maps, part of that ongoing project is to resize the maps for these fighters to be powers of 2 in their dimensions, though from what I hear, something like 512 by 1024 is alright too.