I think they should be less rounded and more of a random sprawling shape.
This could be dictated by elevations. Its a major pain to build on a hill or slope, look at a city like Seattle, it is built on many hills and it is a major pain to make level plots to build houses and buildings on. So instead it would be easier to build around the hills and elevation changes. All animals are lazy and will take the path of least resistance, we humans are not so different ourselves. If we have the choice to build up the hill and spend all the extra time and energy leveling the ground or are we just going to build around the hill. I would build around it unless I had no other option but to build up the hill.
But all in all for the first time implementing a city maker this is outstanding! I am very exited to play in one as an adventure. I hope there are guards because i want to rampage through the city with a gang of bandits, or raid the city from a hidden bandit encampment.
Also looking over the map some more if toady could make little narrow (1 tile) pathways through to the spaces encompassed by buildings that has no access. These could be used as 'dark alleyways' for all kinds criminal and shady activities.