Systems, apparatus and methods for preparing assistance data in a location server from coverage report messages of one or more access points from a plurality of mobile devices are presented. Several mobile devices each collect information from and about one or more access points. This crowd-sourced information is sent from a mobile device to a location server and may include ranging information (such as RSSI or RTT) and/or broadcast information (such as broadcast position and/or transmit power level) and/or computed information (such as path loss). Using this crowd-sourced information, the location server may form assistance data for an assistance data database, which may later be tailored for and send to a specific mobile device.