GPS and other signals aren't continuous, they all use dead reckoning to fill in the blanks in between. This was even more of a necessity with early smartphones

GPS and other signals aren't continuous, they all use dead reckoning to fill in the blanks in between. This was even more of a necessity with early smartphones and navigation systems that only had GPS; nowadays they can use a combination of GPS, GSS, Gallileo, GPS and wifi networks. The latter was a secondary goal of the Google Street View project, matching GPS / location with wifi signals.