<s> thanks Katto....I only have CC2 but I would have thought that it would be quite makeable in CC3.

RedEpic, thanks! Serif Drawplus has a vector scatter brush where you can load vector objects and it sprays them on the page. That's what I used to make the buildings. The vector objects came from Alfar's context free file which is on the site. Then it was a case of drawing in all the roof lines by hand which took a bit of time.