Comment by joebambino

Not advocating for or against Google but GPS is extremely power intensive --> battery life. AGPS (and PGPS) is better but still power hungry and difficult due to antenna inefficiencies and extremely small signal levels. Wifi is much better in terms of power envelope and is ubiquitous in urban environments where GPS is challenging. Dead reckoning is much better than it used to be but is difficult because IMU noise is integrated over time and only gives relative location not absolute.