ing model abstracts over various types of positioning systems and incorporates the capture of uncertainty, serving as a foundation on which developers can apply sensor-fusion techniques. Our programming framework, LOC8, sits atop the space and sensing models, providing a rich API for querying location data and exploring its many representations. Requirements A location model should support location data representations from different positioning technologies and extensible metadata descriptions. Many well-known systems can report an entity’s coordinate or symbolic position, from GPS and Active Badge to more recent systems such as Ubisense and the fingerprint-based positioning system.2 Beyond these are less conventional and less expensive methods of reporting an entity’s location. For example, a Bluetooth spotter, which can detect the presence of mobile phones, PDAs, and laptops, might position a device within 10 meters of a known point. We can use this information to infer the devi...