I suppose the best way to know your community is to get out there and meet them. But the census data can also tell a lot. Earlier this year I found an analysis of Mitchell's Plain from the 2001 census that was extremely helpful. Now there are two other resources from the more recent 2011 census.
The Cape Town City website has all sorts of analyses that are most helpful. I have used the one where data is analysed by suburb to check out the Parow area where I will be working next year.
A fun one that covers the whole country and summarises the census into dots on a map can be found at dotmap.adrianfrith.com It is a pity that the first choice on this one is to look at things by race. I found language fascinating and household income interesting too.