Companies such as Google, Apple, and Skyhook use information gathered from users' mobile devices about cell tower and Wi-Fi access point signals, as well as the Wi-Fi signals of other companies and households, to determine location. These companies compile the precise locations of these signals into large databases, which the companies may then license to other entities such as application developers. An application installed on a mobile device can obtain location information by querying one of these databases, which will use its knowledge about those signals' locations to return the device's location. The database can also use location information sent by the device to update its records. If there are any new signals in the device's vicinity or any old signals that are no longer broadcasting, the database can incorporate those changes in its records. While the exact degree of accuracy ultimately depends on how many signal points are near the device when it queries a database, companies use crowd-sourced positioning because it provides accurate location data quickly, and because it does not rely on GPS technology, which is not available in all mobile devices.