Large amount of unused space in map_icons.png texture file

The file map_icons.png contains a massive amount of unused space, which seems unneccessary.

This could be fixed by simply shrinking the file dimensions (to 32x32 rather than 64x64), but a better solution would be to split up the file into individual textures, as has been done for several other texture sheets (terrain.png, items.png, particles.png, kz.png and inventory.png).