Welcome to the Guild Fregius! There are a few very good town and city map tutorials here, most of which have been made for Photoshop. If you have Photoshop, you are in business. Just check the tutorials section (I'd start by browsing the "Tutorials in PDF format" sticky) or use the search filter. If you don't have Photoshop, you can download GIMP, a powerful free Graphics program. Unfortunately there aren't any town/city tutorials written for GIMP, but with a bit of work you can try to translate the steps in the PS tutorials to GIMP. Best wishes on your project.