Here's a link to a hand-drawn city map I created for Paizo Publishing, a couple years ago, that depicts a city of 180,000. Just to give you an idea of what such a large urban sprawl might look like. At your existing walls and described scale, I don't see how 25,000 people are going to fit that space. Consider that the average sized building in my linked map has an estimated 50 people in each, as extended families and servants in each one.