Using GPS

The primary purpose of a GPS receiver is to receive the signals sent by GPS satellites and then determine current position via triangulation. These positions can optionally be saved in the GPS receiver memory, either as single waypoints or as a series of points forming a track. Both waypoints and tracks can be later uploaded to a computer. Alternatively, waypoints and tracks can be downloaded to the GPS receiver, to allow displaying distance and direction of the waypoint/track from the current position. A trailblazer can thus record a trail using a GPS receiver, publish the track as a GPX file, and other people can then download and follow this track using their GPS receivers. GPS thus makes navigation by compass obsolete.

Mapping GPS's additionally display a digital topo map, along with the track and current position, thus making paper topo maps obsolete. In practice, carrying a compass and paper map is often still advisable, since GPS, like all electronics, can fail in the field. Also, mapping GPS's have very small screens and low-resolution, and thus are cumbersome to use for route planning and getting an overview of the area compared to paper maps.

GPS loaded with GPX track file can be very useful for following snow-covered trails, or for situations where it is frequently necessary to deviate from the trail, then find the way back to the trail further on, and yet the trail location is not obvious due to featureless terrain (a flooded swamp, for example), or for situations where where there is no paper map available with the trail marked, such as for many hiking trails in Spain. It is not necessary to have a mapping GPS loaded with topo maps to use track files, though of course such maps help (at least if they are accurate). All that is required is for the GPS to display current position versus the track, so that you can see when you are deviating significantly from the track and which direction to move to get back to the track.

Another handy use of GPS is to mark a waypoint so as to return to a location after wandering around off-trail. For example, I sometimes make camp in the middle of featureless desert sagebrush, then wander off to explore. The GPS plus waypoint allows me to confidently find my way back to my gear later.

GPX track files can be edited with GPX_Editor (works best, though has some bugs) or GPS Track Editor (doesn't work so well). Editing means getting rid of off-trail trackpoints (due to bad GPS reception or to deviations off trail to eat lunch, explore, etc), consolidating trackpoints along straight segments, merging and splitting GPX files, etc.

GPS Visualizer and ITN Converter allow converting between GPX and other formats (such as KML and PLT).

To merge IMG map files (such as those available from Open Street Map), use GMapTool.

When bicycle touring, I mostly correlate between the road network shown on the GPS map and the road network on the paper map to find myself on the latter, rather than using the lat-long position shown on the GPS to find myself on the paper map. This is because my paper maps for bicycle touring are small-scale (1:400K or thereabouts) and the lat-long grid is confined to the edges of the map, so that finding myself on the paper map using lat-long position is difficult.

Many paper maps lack a GPS grid, but this doesn't mean GPS can't be used with these maps. Just obtain a GPS positional fix at a known location on the map, such as the intersection of the trail with a road. Later, compare GPS coordinates at this known location with current GPS coordinates to find current location on the map. It helps to use UTM format when doing this, since calculating distances with UTM is much easier than with latitude and longitude.

Sources of GPX tracks: WikiLoc, GPSies, Waymarked Trails, WanderMap, Euro-Senders. is huge source of GPS links.

Graph showing positioning error due to using wrong datum. Using WGS84 (effectively equivalent to NAD83 in United States and ETRS89 in Europe) instead of NAD27 or ED50 gives up to 200 meters error. This about what I have noticed in the field when I used wrong datum with large-scale maps. is a source of free maps in Garmin format. has lots of good info about GPS.

Review of GPS apps for smartphones.

Etrex 20 dedicated GPS receiver

Etrex 20, purchased from REI. 95g for GPS receiver plus 20g for carrying case. There is also a plastic bracket to allow attaching to bicycle handlebars, also 20g.

Can be used with 2 AA non-rechargeable lithium, alkaline batteries, or rechargeable NiMH batteries. Either alkaline or fully charged 2300 mAh NiMH batteries will typically power the Etrex 20 GPS for about 24 hours, or 3 days assuming 8 hours/day of usage, moderate weather conditions. I am not sure about hours of usage with lithium batteries. Based on the spec sheet at, they should last at least as long as alkaline or NiMH.

Standard-A to mini-B USB cable allows attachment to computer, for downloading firmware updates, downloading maps, and uploading/downloading GPX files.

The Etrex 20 came with a belt hook, which I used for while to hook the GPS to the strap of my neckpurse. However, this belt hook is not very secure and allowed the GPS to fall off, almost causing me to lose it. So I threw the belt hook away and stored the GPS inside the neckpurse thereafter. Once I got in the habit of always putting it in the same place in the neckpurse, it became as easy to retrieve as when using the belt hook to attach it to the straps of the neckpurse. The belt hook might provide a secure attachment with thick leather belts, rather than the thin webbing strap on my neckpurse. There is also a bicycle handlebar mount available, which is very secure. The carrying case is important when carrying the GPS in the neckpurse, so as to protect the easily scratched screen, though it does make the device somewhat more difficult to read, especially in wet conditions when the plastic of the carrying case fogs up. When carrying the device attached to bicycle handlebars, there is less danger of the screen being scratched, so I don't use the carrying case then.

Additional cost of Etrex 30 versus Etrex 20 not justifiable for most people, in my opinion. Better to spend that money buying good digital topo maps to load on the GPS. Etrex 30 has barometer/altimeter, but this is unnecessary if the GPS is loaded with topo maps, since these show the exact altitude as part of the topo information. Also, altitude given by GPS satellite triangulation is probably adequate for most people. Etrex 30 also has electronic compass, which I see as being of marginal value. Avoid the Etrex 10, which does not support adding maps.

To create GPX files, to allow other people to follow trails for which there is no paper map available, I set the GPS to record automatically and save track files daily. The Etrex 20 allows up to 10,000 points per track, but my tracks tend to average about 2500, or about 5 times/minute assuming 8 hours of recording (I have the GPS set to automatically adjust the recording rate based on trajectory, so that it records less frequently when walking in a straight line, and more frequently when making lots of direction changes). I doubt I would ever walk longer enough in one day to exceed the 10,000 limit. (If that limit did pose a problem, I could set the Etrex 20 to record less frequently.) The Etrex 20 is capable of storing up to 200 track files with 10,000 trackpoints per track file, which is plenty capacity for my 90 days or shorter trips to Europe, which is when I might want to create GPX files.

The Etrex 20 is rugged if not abused, but accidental abuse is always a possibility outdoors. For example, dropping the GPS on a rock so the screen cracks. Given my dependency on GPS these days, and the difficulty of replacing a broken or lost GPS, some sort of backup plan is necessary. Either carry a spare GPS unit, preloaded with GPX tracks, or use GaiaGPS or similar app on a smartphone as replacement for a dedicated GPS unit (more on this below).

[Update as of 2014: Sure enough, my Etrex 20 failed after several years of usage: two long hiking trips in Spain plus seven long bicycle tours, for a total of about 150 days hiking and 400 days bicycle touring. The failure actually occurred at home, while I was playing around with adding maps, but it might have failed on tour. The device was beyond the 1-year warranty and repair cost was $90 plus shipping to Garmin, versus buying a new one for $180. I decided to buy a new one.]

I had a problem with my Etrex 20 during my Spain 2013 hiking trip, in that it appeared to lose track data if I let it freeze at night with the track data unsaved. The GPS was set to record and save tracks automatically. There were also some cases where the GPS did not show the Spain maps when I turned it on initially. If I turned it off and then back on, it did show the maps. There were some firmware updates when I got back from this trip. During my 2014 Spain Hiking trip, I saved and archived track data each evening just before turning the GPS off. Either because of this or because of the firmware updates, I had no problems with data loss on this trip. Saving track data daily also organizes track information by day, which is helpful when later editing GPX files, so is a good idea I've decided, regardless of whether it helps avoid data loss or not.

A micro-SD card with 1:100K USGS Topo maps for the lower-48 United States was included in the Etrex 20 bundle. These maps have numerous errors with respect to the road network. Supposedly, these Garmin 100K topo maps are based on the US Census TIGER road database, whereas Garmin licenses the Navteq road database for use with its 25K maps.

It is possible to convert free Open Mapping Project topo and road maps to Garmin format and then download to either the 2GB built-in memory of the Etrex 20, or to a separate micro-SD card inserted in the Etrex 20 card slot. I tested this capability at home, using topo maps for Greece, and it worked well enough, however I never tried using these maps in the field. Do an internet search for more info.

AA Batteries for use in Etrex 20

Standard 1.6V non-rechargeable lithium batteries (30g for 2 AA) work better than alkaline batteries (50g for 2 AA) in sub-freezing weather and are also have longer shelf-life. Avoid 3.6V rechargeable lithium, which will overload the GPS electronics. Rechargeable NiMH batteries (55g for 2 AA @ 2300mAh) work better than alkaline in cold conditions, though not so well as lithium, but supposedly don't work well in very hot conditions. I'm not sure what is meant by very hot. I experienced no problems with NiMH batteries in temperatures of 30°C/86°F.

When using lithium batteries, the charge level shown on the GPS device will remain at the full level until right before the batteries die, whereas the charge level is shown more accurately with alkaline and rechargeable NiMH batteries. When using the GPS to record GPX tracks, it is important to keep tabs on the charge level, so that the GPS doesn't die unnoticed while recording. Alkaline or rechargeable NiMH batteries are thus better for track recording. If using alkaline batteries to record GPS tracks in cold weather, be sure to keep the batteries warm.

Currently, I use the Apple compact NiMH AA battery charger (55g) with the 2000mAh batteries (50g per pair) included with that charger. This system worked well during my 2016 hiking trip in Spain. Previously, I used an Energizer Smart charger (115g) with Energizer 2300mAh Recharge Power Plus batteries (55g per pair). This combination was heavier and less compact than the Apple system, but otherwise also worked well.

Smartphone plus GPS app as replacement for dedicated GPS receiver

I tested using Android smartphone plus GPS app plus offline maps during 2017 (GaiaGPS app) and 2018 (Locus and OruxMaps apps) hikes in Spain and Bulgaria. System worked well enough that I will continue using in future for hiking (still plan to use Etrex 20 dedicated GPS receiver for bicycle touring).

Of the apps I tested, Locus was best for my purposes, mainly because better interface. Note that neither Locus nor OruxMaps is available on IPhone, whereas GaiaGPS is. See pages for Spain and Bulgaria for details of maps I used for the various apps.

First problem I encountered with smartphone plus app system is that track recording tends to run down smartphone battery. Be sure to bring along external batteries (described on Smartphone page) if you plan to use a smartphone as your GPS unit, especially if you plan on recording GPX tracks. During my 2017 Spain hike, without recording GPX tracks but using GaiaGPS constantly to check position, and keeping screen lit 2 or more hours daily for reading ebooks and editing text files, and playing music and other audio files via bluetooth to an external speaker 2 or more hours per day, and doing a small amount of cellular usage (checking email, a few phone calls), I almost completely drained a 10000 mAh external battery but still had 65% charge on smartphone after 4 days hiking and 3 nights camping, using my Moto X 3rd Gen smartphone running Android Marshmallow. It would thus be possible to go over a week between hotel stops with two 10000 mAh external batteries, at this rate of usage. I am not sure exactly how much power GaiaGPS consumes when recording GPX tracks, but it is obviously more than when not recording. Locus app appears at least as efficient as GaiaGPS in terms of power consumption. Not sure about OruxMaps.

Second problem is that smartphone capacitive touch screens tend to act flaky when wet, so even if phone is water-resistant, as it should be for use as a hiking GPS, you will need some way to dry screen each time you need to touch it to zoom, pan or perform other operations. I was able to get by wiping screen against my shirt few times I encountered rain/snow (most of my hiking is in dry conditions). If planning to hike extensively in wet conditions, you would probably be better off with Etrex 20, whose performance is same wet as dry, rather than a smartphone as your GPS unit.

Third issue is that, because electronics can fail, spares are essential for critical items. GPS is critical for me, since I no longer carry paper maps when hiking in Europe. So be sure to carry backup smartphone (loaded in advance with GPS app, offline topo maps and GPX tracks, and with fully charged battery) in case primary fails. (Obviously, same need for backup exists with dedicated GPS receivers, since these are also electronic and thus can also fail unexpectedly.)