It really depends on what you are looking for. Are you trying to generate road networks? Do you want city building assets/brushes? The style of city map which you are looking for will also dictate what you need to some degree.

I believe Campaign Cartographer and Inkarnate have city mapping features, though I haven't used either. Many people use wonderdraft for cities as well even thought it isn't designed for that purpose. Personally, since I don't use many pre-created assets or brushes, I prefer to work in Gimp since that give me a ton of flexibility, but obviously it is not specifically designed for mapping.