Hiking with offline maps on Android

A map that loads as you look at it stops where the signal stops. In town that is never a problem: the map is there before the phone is out of your pocket. In the mountains the signal goes just where the path forks, and where the map should be there are grey squares around your position.

The answer is a map that is downloaded before you set off. walker, the walk, hike and ride tracker I make for Android, is built around such maps: it never loads a map from the internet as you go. Most of what follows holds for any map app.

Why a map that needs signal lets you down

There is often no signal. The Austrian Alpine Club (ÖAV) says so plainly: in the high mountains there is mostly no mobile data, or only a poor connection. Deep valleys and the far side of a ridge are no better. A map that loads over the internet has nothing to show there.

Abroad, the map can cost money as well. Inside the EU, and in Iceland, Liechtenstein and Norway, you roam like at home. Outside them, data roaming can be expensive, and it is worth checking the price with your provider before you travel.

The hunt for a connection also costs battery. The ÖAV advises turning mobile data off for a tour, so that the constant attempts to connect don't become a power drain. An empty battery on a hill is a much bigger problem than a missing map.

Your position doesn't need signal

This surprises many people. The GPS receiver in your phone listens to satellites. It doesn't need mobile data to work out where you are. Mountaineering Scotland advises putting the phone in flight mode to make the battery last a lot longer, and says the GPS will still work, so you can still find your way.

So the position is not the problem. The map under it is. Once the map is stored, you can switch off mobile data, or turn on flight mode, and still see where you are.

Prepare at home

Download before you leave

Maps are large. Download them at home on Wi-Fi: every map you might need, so that nothing on the hill depends on mobile data.

Take more than the route

Plans change. You may take another way down, look for a hut, or turn back early. Save the map for a generous area around your tour, and more than one kind of map if you have them. Include the valley you start from and the ones next to it.

Charge everything

The German Alpine Club (DAV) says to charge the phone fully before a tour and to carry it close to your body, where it stays warm. On longer or colder tours, it adds, a power bank to recharge the phone is very useful.

Test it before you go

Do this at home, the evening before:

1. Turn on flight mode.
2. Open your map app.
3. Zoom and scroll along the whole route, from the car park to the summit and back, and a little way beyond.

If any part is grey or blurry, it isn't downloaded. Get it now, while you still have Wi-Fi. Then turn flight mode off again.

What an offline map can and can't do

Once the map is downloaded, three things keep working:

• the map itself, in every area you downloaded;
• your position on it, from GPS;
• recording your walk, in an app that stores the track on the phone.

Without a connection, three things stop:

• anything outside the areas you downloaded;
• features that ask a server, such as weather forecasts or sharing your position live;
• phone calls and messages, unless you find signal.

For emergencies there is one thing worth knowing. According to ÖAV advice reported by Vorarlberg Online, a call to 112, the European emergency number, connects through the strongest network available. That advice also prefers flight mode to switching the phone off, so you can react faster in an emergency. The DAV adds a caveat for anyone out alone: in flight mode, the phone can't be located during a search.

An offline map is also no replacement for a paper one. The DAV's rule is that a paper map should always be in the rucksack as a backup. It needs no battery and no signal.

How walker does it

walker's maps are map regions kept on your phone, so the map works anywhere once a region is downloaded. The help page's Maps section has the details.

To add one, open Map packs → Add region and choose an area: a state or province, a district, or exactly the part of the map on your screen. walker shows how large the download is before it starts. You can keep using walker while it downloads, and a download that is interrupted resumes where it stopped.

The maps are built on OpenStreetMap. Before you download, walker shows what the map server learns: your internet address, the region and the time. It never learns your position or your walks. Privacy & storage lists every time walker went online.

If you open walker somewhere no downloaded region covers, the map says so, and its banner leads to Map packs. walker never checks for newer maps by itself. When you want to, tap Check for updates there.

For hilly ground there is more. Each region in Map packs has an optional Terrain download: the heights of the ground in that region. walker uses them to make the heights of your walks more accurate, and from them it draws hillshading, the shading that shows the slopes, and contour lines on the phone. They show in the Topo layer, contour lines every 10 m, labelled every 50 m. How the phone draws them is in contour lines and hillshading on the phone.

For Germany, the layers button on the map offers two more. TopPlusOpen is the official topographic map from Germany's federal mapping agency. Aerial is the German states' aerial photos with the map's paths over them, and covers fifteen of the sixteen states. For both you frame an area on the map and choose the detail, 3 m, 1.5 m or 0.75 m per pixel, and walker shows the size before anything goes online.

Every layer comes from a download you start yourself, best done at home on Wi-Fi. On the trail, the map loads nothing from the internet. To keep the recording itself going for hours in your pocket, see when Android stops your tracker.

A checklist

• Download the map for your route, and a generous area around it, on Wi-Fi.
• Test it in flight mode: scroll along the whole route.
• Charge your phone, and pack a power bank for long or cold days.
• Keep the phone warm, close to your body.
• Carry a paper map as well.
• On the trail, flight mode saves battery, and GPS still works. Alone, remember that nobody can locate your phone while it is in flight mode.

Signal in the mountains comes and goes, and you have no say in it. The map is up to you: the one that works when the path forks is the one you downloaded and tested at home, the evening before, while it didn't matter yet.