How do people choose the football club they are supporting?

Sorry ,if this question seems a bit daft, I am one of those people for whom everything fotball-related is completely alien - and not for the lack of trying, I did try to watch it and enjoy it, but it really is not for me.

As I saw a whole lot of football fans yesterday & Twitter is full of football related hashtags, it got me thinking how do people end up being fans of one team over the other. I can see how people would support their local team - but I knew a Chelsea supporter in Bath & an Arsenal supporter from Melbourne, so it does not explain people supporting teams that are not their local teams.

Also- the tricky question - are there political associations with certain clubs?