New hikers often ask me if they should buy a GPS (Global Positioning System) receiver (*1) as part of their start up and essential gear?
My answer is always emphatically: “No. – Spend the money on a Personal Locator Beacon, that’s more use to you currently…”
What have I against GPS?
Actually I have nothing against GPS units in the outdoors, but only in the hands of experienced Hiker’s who recognises the device is as just another Navigation tool to always be used in combination with the basic Navigation skills including Positional Awareness, Topographical Map and Compass.
With out the basic Navigation skills, the inexperienced GPS user has no way of verifying the accuracy of the GPS, particularly when they are unaware that;
- The GPS never knows exactly where you are, rather it requires you to interpret its recommendations against your knowledge (Never just Trust your GPS)
- A GPS only focus is on pointing you where you want to go, it doesn’t understand the limits of being human, your job is to work with the GPS not believe its every word… ( unlike people we see daily on our roads, clearly using a GPS!)
- The “signal” (satellites available at that point in time)is degraded-(along with the position accuracy) by quite a few things in the outdoors.
- An electronic device is dependent on battery power, as well as susceptible crashing and loosing loaded way points for no particular reason.(*2)
How do GPS work
The Term Global Positioning System was originally the name of the US developed satellite based precise positioning system, but has now become the generic term for all systems.
Orbiting the earth there are a collection of satellites (including the US (GPS) and Russian (GLONASS) which constantly transmit a signal back to earth.
Put simply, your receiver uses these signals and some complex maths to work out its approximate position relative to the known position of the satellites and earth’s surface.
Despite this system, quite a number of variables can still degrade the accuracy of the calculations including;
- If you are moving
- The type of receiver
- The type of antenna /type of device. (see below)
- Signal strength
- How many Satellites are “visible” to your receiver in that chunk of sky.
- Minute errors in the signal form the satellites or your receiver magnified by distance
- The Ionosphere(up in space) blocking the timing signals
- Organic and Inorganic obstructions to the signals: Narrow valleys, Rock, Dense bush cover, Concrete, Steel(buildings)
A couple of common position Errors
While most modern GPS can try and predict where you are based on;
- Where you were before
- How fast you were moving
- The direction you were moving in
They still can only make an approximation(*3) of your position to within 3 to 40m + depending in the type of receiver.
As you can see in the picture above, the position of the track log recorded on the way up this track(at the red line) is 40m different from that recorded on the way down, despite the fact we were walking on a narrow well worn track..
While 40m might not seem like a lot, I can assure you if you were trying to find the track using only the GPS, it would be very possibly to walk 5-10m parallel to it or even cross over it and not even see it. (*4)
Not all GPS are Equal
As technology advances we are seeing an increase in smart devices that also include GPS chips for various purposes, while many can navigate pretty well around the city or in open air when compared to a dedicated receiver their does tend to be a greater error, in back country conditions.
The picture above was recorded on the same day under medium bush cover walking up a steep ridge line;
- The hand held receiver (Track log (b)and Smart phone (Track log (a) were carried 30cm apart at chest level
- The majority of this section of track the GPS was recording a 7m accuracy
- The GPS was set to record track points at 10m intervals and the Phone at “most often”
- The closest the phone came to the GPS track was 7m, the average being 20-40m away
(The Track printed on the map(c) is only a guide of the route – on most modern Topographical maps they seem to be pretty accurately placed however.)
Before you get a GPS
The most important step is to fully develop and practice your foundation navigation skills until they become second nature;
- Learn to read and navigate by a Topographical map and compass.
- Develop your own awareness of where you are in the terrain (positional awareness) and “common sense.”
These basic skills used together give you a greater degree of accuracy and help you automatically detect and correct errors including those from using Global Positioning devices later on. (and the basic skills always work even when the batteries are flat)
Learning GPS Lore
If you have go ahead and buy a GPS , then another useful learning tool is playing a GPS game like Geocaching, which will assist you in seeing the strength and weakness of the device before you need to depend on it.
- The use of GPS devices and smart phones as navigation aids
- How does GPS work
- Why back country GPS units are overrated
(*1) While the name GPS is now used to describe the device, it has also generally come to represents the USA technology(originally called NAVSTAR) while Russian system is known as GLONASS. Most modern hand held GPS and Smart phones have both systems included.
(*2) GPS Crashes are sufficiently common for no particularly reason it can be wise to carry any important way points on a USB drive or smart device along with the GPS cable and OTC cable with a knowledge of your Devices file system so it can be restored.
(*3)While public GPS Receivers are not entirely accurate, those used by Surveying, Construction and Military GPS can extremely accurate, in the region of cm’s.
(*4) this is the importance of always using your GPS receiver as just another tool in your navigation tool box – see the post on Staying on the track- basic.