Navigating with phone and GPS: offline maps, battery, limits

GPS is really just one of several satellite systems; together they are called GNSS. They include, for example, the American GPS and the European Galileo. Modern phones usually receive several systems at once, which can improve positioning in difficult terrain. The receiver needs a clear view of as much sky as possible.

The mobile network only helps the phone get started faster: with signal it gets extra information that lets it find the satellites more quickly. Without signal the first fix can therefore take a little longer – but it still works. On most devices satellite positioning stays active in airplane mode, too.

What does not work without signal: loading new map sections, calculating routes online, fetching weather. So preparation includes saving the whole trip area plus a generous margin around it as an offline map – and testing it beforehand in airplane mode.

The bright screen is usually the biggest power drain. Someone who keeps the map open all the time empties the battery much faster than someone who just checks briefly at junctions. Radios that keep searching for signal cost extra energy too – especially in areas with poor reception.

Cold is the second big enemy. Batteries deliver less power when they are cold. A cold phone can suddenly switch off even though it showed a decent charge a moment ago. So carry it close to your body in an inside pocket; it can often be switched on again once it has warmed up.

There are no fixed figures for battery life – it depends heavily on the device, the age of the battery, the app and the weather. Instead, set your own limit, for example a charge level below which the phone is only for emergency calls, and plan to turn back before you reach that limit.

The position can be inaccurate when little sky is visible: in narrow valleys, right next to rock walls, in dense, wet forest or between tall buildings. The dot then sometimes jumps around or lies beside the path. The accuracy shown is not always correct.

Apps often calculate routes automatically. In doing so they can suggest paths that are closed, overgrown, far too difficult or dangerous. Map data in apps can contain errors, especially for small paths. So check suggested routes on the map before the trip: how steep does it get? Are there rocks, streams, glaciers?

And finally, the technology tempts people to forget how to read a map. Anyone who just follows the dot often does not know where they really are in the terrain – and is suddenly left with no orientation at all when the battery dies.

A flat battery takes away navigation and the emergency call at the same time. So: start fully charged, pack a power bank with a matching cable, save power and set an emergency reserve. On long or remote trips the phone should never be your only means of navigation – a paper map and a compass are light and need no power.

Practise at home where your app shows the coordinates. In an emergency you can then read them out calmly. In many countries phones also send their location to the emergency centre automatically during an emergency call – but do not rely on that alone; state your position anyway. The local emergency number (112 in the EU) can often be reached even when your own provider has no coverage but another network is available.

A dedicated GPS unit with replaceable batteries is often more robust, usable with gloves, and keeps the phone free for emergency calls. The same applies: load maps beforehand and practise using it beforehand.

The evening before the trip: load the offline map for the whole area, switch on airplane mode and check that the map still displays. Fully charge phone and power bank, pack the cable. Look at the route once on the map and compare it with the terrain (contour lines!).

On the way: dim the screen, close unneeded apps, use airplane mode when you do not need signal, and only look at the map at important points. In the cold, put the phone in an inside pocket. Recording your route (a track) can help you find the same way back – but it costs power too.