OK, here is where I am now.
Cambridge provides GIS layers. I can look at them in Cambridge-provided views, but I can't choose all the layers I want.
This is a good starting point. It shows layers footpaths, buildings, roads, sidewalks, other paved surfaces.
I could take a screenshot and import as background map into OCAD.
Matt says if I send him shape files he can import into OCAD11 and then export a map in OCAD10 that I could use. But he would have to do work to tell OCAD11 what symbol to use for each of the things in the layers. That seems like a lot.
What I want is something like what is shown in the Cambridge CityViewer linked above, plus additional layers (trees, fences, ...)