Editorial. We extrapolate the urban vs. rural balance from the trailers. Specifics aren't confirmed.
What the trailers suggest
Vice City has more total screen time than the rest of Leonida put together. However, this does not mean it takes up over half of the map. Marketing videos are biased towards dense urban footage.
The aerial frames indicate that the map balance is probably closer to 1/3 city and 2/3 everything else. This is an editorial estimate, not a measurement.