City utilization range

I'd like to change the range that a city can reach for its workers - is that possible without major changes, especially to the "City
Map" in the Overview tab?

Ideally, I'd like to see that distance increase with city size: size>4 = range 1, size>8 = range 2, size>16 = range 3, etc.  I
suspect that would be more work tho.

Anyway, is it possible to change that range in any sort of easy manner?