Maybe page content and location, or at least location in a broad sense (down to a city or state level) to allow for small niche businesses to buy relevant advertising. I.e. The local model train shop buying ad space for users of a model train forum that are conceivably close enough for them to actually go there
Location data seems like a better fit for maps, which would tie in to searches for X, and maybe include some sort of coupon that when used also gave a small kickback to the route which the customer got it via.
