I have however seen people get around this by making their own version of the map; often opting for a map that more closely resembles the true relative position

I have however seen people get around this by making their own version of the map; often opting for a map that more closely resembles the true relative positions of the stations. Naturally this CSS map is an almost 1-for-1 copy of the original. But how far would it have to diverge to not be copyright infringement? Different colours? Use rounder angles ?