Wi-Fi Positioning System (WPS) is a term pioneered by Skyhook Wireless to describe its Wi-Fi-based location system.
It is now widely acknowledged, however, that Google, Apple, and various phone makers and carriers have compiled their own very extensive databases of Wi-Fi access point locations by correlating Wi-Fi access points with GPS locations of cell phone, smartphone, and in some cases, tablet computer users. Anonymously determining users' location in this way is part of virtually every cell phone terms-of-service agreement, though most phones allow the user to turn off location services.
Google has added a way for Wi-Fi access point administrators (that includes you, if you have a home Wi-Fi, or control your office Wi-Fi) to opt out of its WPS database. Simply add "_nomap" to the name of the Wi-Fi network, and Google will not map it.
WPS may be combined with cell phone tower triangulation and GPS to provide reliable and accurate position data under a wide range of conditions, including among tall buildings and indoors, when GPS signals may be weak or intermittent.
Limitations: WPS does not work when out of range of Wi-Fi signals, and the Wi-Fi hotspots database must be constantly updated to keep up with Wi-Fi hotspot changes.
See also fake gps.