The My Best Segment Site

I entered my zip code into the site thats supposed to tell me exactly what kind of people live near me and i was surprised at how kind of on it was. I didn't think it would be anything near what the city of Somersworth was like but it was it got it almost spot on. The older Somersworth community with a bit of a rustic feel to it, as I was reading i could picture people i know that fit into those categories.  It's interesting to think that there are sites that can do this sort of thing. My question is how do they do it? Do you they send a crew or take surveys? Whatever they're doing it's working at least it is here.  It's interesting to think about what you could do with information like this, marketers could get there advertising to the people they want to and not those who would disregard it. Tools like this could be extremely useful to someone trying to find a certain group of people or maybe someone just doing research. The site could be better though I think, imagine a site that not only has just some general description of the people that live in an area but a site that has fairly detailed information about the area. Where they shop, when they shop, what they're buying, the type of people that live there, demographics, etc. all information a budding business or a huge corporation could use. Do you think a site like that could ever exist? why or why not.