If you want to time your running and walking intervals, you can use a watch or other device that beeps to signal when you need to switch.

That way, the device responds quicker than it would if it had to download the data for triangulation each time from Apple, or wait a minute or so for the faint signal from a passing GPS satellite.

A device that is similar to a microprocessor, except that the internal CPU has been optimized for use in applications involving discrete-time signal processing.