All modern smartphones incorporate a GPS chip and use this, together with a variety of other methods, to determine a user’s position. In urban areas the smartphone can establish the position with very considerable accuracy – for a summary of the methods used see the PCWorld article available here.

Outside urban areas – and especially in remote areas of countryside – smartphones tend to deliver poor accuracy as they have to rely almost exclusively on satellite and cell ID data. This is an issue because smartphone aerials are not optimised to receive satellite signals, and cell ID data are not much use unless the phone can receive signals from more than one cell. It is in these circumstances that dedicated GPS receivers come into their own.

Further issues to mull over are as follows:

1. Unlike dedicated GPS units, smartphones are generally not durable or weather resistant.
2. Battery life is severely compromised when using a smartphone as a GPS. Smartphones do not have removable batteries so a USB battery pack is required for long trips. Dedicated GPS units have lower battery drain and replaceable/rechargeable batteries, and can accept readily available primary cells in an emergency.
3. Smartphones are touch screen devices so in very cold weather one has to remove one’s outer glove to operate them. Touchscreen gloves are of course available but these are generally lightweight and unsuitable for very low temperatures or where there is substantial wind chill. Most (though certainly not all) GPS units have conventional buttons to control their features.

As a matter of interest, Garmin claim that their receivers are positionally accurate to within 15 meters (49 feet) 95% of the time and that users will see accuracy within 5 to 10 meters (16 to 33 feet) under normal conditions. As regards elevation, Garmin claim that a calibrated GPS relying on satellite data alone will deliver accuracy of +/- 122m (400 feet) given a strong GPS signal. Those devices fitted with a barometric altimeter should, with proper calibration, report elevation readings ranging from minus 600 to plus 9000m (roughly minus 2,000 to plus 30,000 feet) to within +/- 15m (+/- 50 feet).