Why doesn't gps work without phone signal

Question

If I am driving through the mountains and lose my phone signal my gps stops as well but a handheld gps keeps working fine.

Answer 1

okay i think i figured this one out
yes it is true that the iphone has a dedicated gps recevier and it is also true that some navigation apps like the standard maps app and the garmin navigator need some kind of connection to fetch the map ..
but the gps recevier is a AGPS receiver, this means it has a standard gps receiver but it also uses the cell towers to assist the gps lock and to speed up the locking process. without some kind of conenction to the tower or a wifi connection, a full gps lock can realistically can take 15 or 20 minutes to get, if you do not know where the satellties are. the gps satellites only broadcast once every like 30 seconds? and with 30 of them it means it can take 15 mintues to get them all
the iphone uses the towers and wifi connection to download information on where the satellites are and then looks for them to speed up the gps locking.
so to the original posters question to why his iphone cannot get a gps lock. well yes you might need a connection to get the map, but if you want to get a lock without a cell phone connection / wifi connection to assist you, you just need to wait 5-15 minutes to get it
and to answer why the standalone gps can keep going could be because some gps units keep 3 or more days of gps coordinates. tomtom calls this feature of obtaining gps corrdinates to speed up gps locking, GPS quick fix.
there are also some chipsets like the sirfstar iii that are known to speed up gps lockng