You will run into problems.
SAMP has object limits, so these cities wont be able to be too large, or be close together
You can only have a maximum of 2000 objects at any one time. So, say you're standing in a mapped area, there's a radius of 250.0, in which there can only be 2000 objects
So for it even to be remotely possible, these cities must be away from any other mapping, and spaced well apart from each other