Define different free shipping based on cities.

Hello,
We are going to do local ecommerce, the idea is shipping just only in our city.

But city is big, if user wanted 10$ for 50 km away it's a big problem or if we define free shipping for 50$, we will lose really close small customers. We want to define free shipping based on city.

Normally the opencart idea is Country -> State/Region -> City ( User has to type it), we changed it now user could select it thanks to city based shipping extenstion.

I couldn't figure out, which controller or model I should change. Normally free shipping can have only one geo zone, if multiple I think I can arrange it.

Ultimate Shipping can limit based on city name, or I'll be adding that functionality to Formula-Based Shipping and Free Shipping Plus soon. As long as the city name is filled into the regular City field, then my extension could utilize it.

Or, I believe we've been corresponding over e-mail, and if the postcode is automatically filled based on the city, then any of my extensions can currently utilize the postcode for rates.