In this thread here: City Maps Galore (Pen-n-Paper) is collection of all the city maps I have done on Pen-n-Paper. I have mapped a lot of cites.
For Deestan, I took a Pen-n-Paper map, scanned it (did to post in the above thread ) converted to BMP, and then insert that as a layer in CC3. To see how to do that, follow this tutorial:
[Award Winner] How to Insert a Pen-n-Paper Map into CC3
Then. In CC3, I made a drawing tool for the buildings that would allow me to draw polygons in White, and then outline them in Black. This I use for the buildings, thus allowing me to draw, draw, draw the buildings as I like.
As for cities, a non-planned cities (and a lot of cities were planned, look to the Ancient Egyptians for City planing at it's finest):
There was even an Egyptian city that was physically transported in it's entirety many miles up a river as conditions had changed to drastically at it's original location. Can't remember though.
As it is, most cities usually began as small collections of locals around a primary reason for congregation (a ford in a river ala Oxford England, a an ancient fort (London for Roman Conquests) or castle at an important geographic feature. The town then sprigs up following the lay of the land (easier to build at the bottom of steep hills and along a source of water like a river or lake) and as it grows in size and prosperity a wall may be built to protect the place. Of course a place may continue to grow after the wall has been built in which case a second or even third wall will be built to surround the whole.
In Deestan, the Original city was built as a planned community around the keep which hold a position of prominence at the mouth of a river (the smaller rivers form a bit of a delta). Good farmland, the place grow in size until the power of the nation through use of the enslaved Elementals allowed them to 'build' a new expansion tot he city. Thus the 'Old' city of Deestan has some order to it. With the collapse of the empire and refugees from the holocausts of the region, new communites are forming outside the city walls in a very chaotice fashion. If the regio continues to grow, a new city wall may be built to encompass these outsprawled areas.