Setting Map Scale

There are various RPG systems that utilize different grid sizes for their games. For example D&D has maps where the 1-in grid equals 5 ft, and other maps where the 1 inch grid equals 10 ft. Other game systems also have map scales where the 1 in grid equals 3 ft or 1 yd. It would be helpful if we could set that scale when creating the initial map so all items and terrain automatically scaled to fit that grid size.