Algorithm for location based service

Consider the following situation. Lets say I am standing in the middle of Amsterdam, and I would like to use my phone with GPS device to look for interesting places within 1 KM. How will you found all these places, given that all sightseeing places in Amsterdam are registered in my database, complete with longitude and latitude. So, I will need a calculation that calculate the distance between one location with another given the longitude and latitude. Say there are 1000 sighseeing places in Amsterdam, would it be viable to first divide Amsterdam into multiple areas before calculating the distance?? You can end up with smaller subsets. How is this calculated?? If its ok, then the last step is to make a sort mock-up code in PHP that show how to do the calculation.