Foursquare has great API and documentation about it. Nice thing is that you don’t need to authenticate to use most of the API. But even then you will need to have registered for Foursquare developer. If you need to authenticate foursquare is also using OAuth if you need to authenticate check this.
Now the API I’m very interested is venues. To use it you don’t need to authenticate. So I will just use it without authenticating. So to use it I just download the json information from the API where I pass latitude and longitude as parameters and then use JSON.net and JSON2CSHARP to parse it into nice objects. Classes from JSON2CHSARP:
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