Location-based services (LBS) belong to an emerging class of information services that cater its content to the geographic location of a user. Possible applications include navigation assistance, friend finding, and emergency response. Users are typically envisioned to be mobile and located by possessing a location-aware device, such as a cellular or mobile phone. The availability of location-aware devices is increasing; however, at the time of this writing, there is a limited number of compelling LBS offerings in the United States. Nonetheless, the potential adoption of LBS by a large segment of the population still remains likely, if not inevitable. This presents new opportunities and challenges for collecting, managing, and analyzing geographic information.