Question regarding the population size of a city and I wanted to clarify my understanding of the rules.

If I have on an island a  metropolis size city that has an area containing five regions each at Density level 3.  Would that mean the population size for this collection of regions is 250,000 people?  That does not even include the six other regions with various levels of density which could put the overall city population at 315,000.   That would make it one big island city or as I have it a collection of cities. 

Hey! So the Sense of Scale is to give you an idea for the rough size of the city. It doesn't have any bearing on the rules so you're free to move things as you want. But yes, your calculation sounds about right.