
So my suggeston is to add another index (city coverage index) that will be higher the more coverage of a city your stores (selling the same product) have. And this index should boost demand in your stores in the same way as customer traffic index does.
Example:
1. Selling bread in 4 stores in different places in a city - (bread) coverage index = 80.

2. Selling bread in 4 stores placed near each other - (bread) coverage index = 35.

This index should be computed for each product you selling in a city, based on a stores in which this product is offered. Some products my benefit more from it (like bread), and for other it will not be so much important(like cars). It can be displayed near product's supply/demand like on this picture (or just somewhere as a number):

I posted this because i think that placing 4 stores (selling the same product) like this on picture above is kind of dumb

This is a solution that my brain came with, but feel free to post your thoughts here, maybe you have some simpler solution
