Here's a couple more. * Inertial navigation, using gyro and accelerometer to approximate movement since last known position. * Pressure sensor can give app

Here's a couple more. * Inertial navigation, using gyro and accelerometer to approximate movement since last known position. * Pressure sensor can give approximate Z axis (altitude). This is significant if your X,Y says you're in or near a tall building; combined with the Z, you confirm the building and the floor +/- a few floors.