right mumbo, it really does not matter. but it might be good to use the maya units as a measurement - e.g. imagine one maya unit to be 1 meter. this way you can have accuracy up to 1 mm - should be enough for a city scene ...

p.s.: dont jump on me that you might be able to work more accurate - but if you enter numbers you are limited to 3 digits after the comma (or point) - i am not 100% sure if verts can be places more accurate ...