Collaborative database of Wi-Fi access points spotted by volunteers. Search for a network name (SSID) or the MAC address of an access point (BSSID, for example 3C:A6:2F:00:11:22).

In real life: WiGLE. A network name (SSID) is not unique: thousands of routers share the same one. The MAC address (BSSID), however, identifies a single access point.