[QUOTE]\n[QUOTE="Alan Browne"]\n[QUOTE]\nThere is just no way to keep furiously updating the worldwide\ndatabase all\nthe time without an immense cellular data volume that the users\nwould have\nto PAY FOR.\n\nThe data required is relatively small. In densely populated areas, it\ndoesn't need every single BSSID, just a sampling of them.[/QUOTE]\n\nYep.\n\nThe BSSID is 48 bits (all tolled), add L/L to 1 metre accuracy for\nanother 50 bits. 13 bytes of binary. A bit of wrapper and you could\ndo the whole thing in a very short message - even if the binary was\nrepresented as ASCII hex or the L/L were more sloppily represented.\nMaybe add a few more bits for signal strength for further analysis.\n\nSo phones could cache quite a load of locations and slowly chuck them\nup to Apple, Google and Skyhook every time there was a WiFi connection\nw/o the user noticing much happening. With more and more generous\nbandwidth terms from cellco's, it could also be done continuously in\nthe background in real time.\n\nThe database s/w would just need to validate or improve whatever is on\nrecord or flag BSSID's as "too mobile, too often" to be useful.\n\nAnd I doubt they have only "samplings" as it's very cheap, datawise,\nto grab 'em all!\n\n Beyond that, some intelligent processing could improve the\nposition estimates of the WiFi stations over time.[/QUOTE]\n\nTrouble is that there is no way for an apple\ndevice to accurately locate a bssid that it can see.[/QUOTE]\n\nIf that BSSID is not already cached, then send the BSSID to the server,\nwhich returns the estimated location of the WiFi (if previously seen and\nstored in the database). Of course you need a datalink (Apple's own\nMessages service could serve this - out of sight of the user) via the\ndata plan on the iPhone.\n\nAs to "accurately", if the various reporting iPhones get a reasonably\ndispersed set of locations around the WiFi station, then the location\ncan be estimated as somewhere in the middle. Knowledge of signal\nstrength for each sampling iPhone could hone that somewhat. With a half\ndozen such locations around a WiFi I'd WAGtimate 10 - 20 m accuracy for\nthe location of the WiFi. Of course that is not the location of the\niPhone using the WiFi as an initial source location.\n\nIAC, knowing the position of the WiFi to within 200 metres is enough for\na good first guess and will help the GPS/GLONASS receiver correlate much\nquicker.