GPS - The Myths and Truths - Part 1
GPS navigation systems for Walking and Hiking have their fans and detractors in seemingly equal measure.
Some think a GPS Device for Walking and Hiking is just an unnecessary gadget used by overgrown schoolboys who would buy anything if it was yellow and had lots of buttons to press.
Others consider it to be a valuable navigational aid any serious walker should carry and learn how to use properly.
Below we hope to address some the issues, myths and truths surrounding GPS navigation systems for Walking and Hiking so you can make a value judgement on whether or not walking with a Walking and Hiking GPS Device is for you or not.
GPS Navigation Systems for Walking and Hiking
The Myths and Truths - Part 1
Myth: Forget the map and compass, all you need these days is a Walking and Hiking GPS Device.
Truth: A Walking and Hiking GPS Device is an excellent navigational aid - but only a navigational aid.
You still need to take the walking proper map (the 1:50,000 scale OS Landranger series is usually detailed enough for the remoter areas of Scotland but you'll need the 1:25,000 OS Explorer/Outdoor Leisure Series for most of England and Wales), a good compass - and knowledge of how to use both* (plus a little common sense).
Compass navigation and map reading are basic skills* that you (or your party's leader) must possess if you’re planning to venture into the high mountains.
Using a Walking and Hiking GPS Device all the time in nice weather may lead you into a false sense of security. Suppose, the weather changes or one of your party has a fall and you need to find an alternative route down.
Suppose you dropped your Walking and Hiking GPS Device and couldn’t find it again, or the batteries you just put in were duff, or the US government decides to turn off all the satellites, or one of your pals believes that they’re the work of the devil and froths at the mouth every time you acquire four satellites.
Take and use a Walking and Hiking GPS Device by all means - but make sure you also take a map and compass and check your position with both regularly.
Myth: You can’t go into the high fells and mountains - particularly in Scotland - without a Walking and Hiking GPS Device.
Truth: There is nowhere in the British Isles that you cannot successfully navigate with the proper map and compass. A Walking and Hiking GPS Device is a good and useful navigational aid - but not essential.
Myth: A Walking and Hiking GPS Device will lead you over a cliff.
Truth: It will - but only if you are daft or not paying attention to your surroundings.
A Walking and Hiking GPS Device always points to the target you’ve programmed in (providing you are moving). If you were to follow this direction slavishly, you might well walk over a cliff, or into a lake, or even under a bus. However, since the Walking and Hiking GPS Device always points at the target, when you take sensible avoiding action, it still points at the target from your new position. A new route, therefore, is automatically recalculated for you, and is always being recalculated if you tend to wander about a bit.
If you think about it, a compass has exactly the same properties of being able to lead you over a cliff/into a pond/through the back yard of the fish shop – the difference being that YOU have to recalculate a new route after taking avoiding action.
The trick, with both devices is to only use the GPS when your target is fairly close – less than 500 metres is ideal.
If you’re daft enough to walk off a cliff, down a hole or into a pylon because a Walking and Hiking GPS Device tells you to, then you’re not really sufficiently self-reliant to be in a place where you need to use a Walking and Hiking GPS Device are you?/p>
Myth: A Walking and Hiking GPS Device is accurate to within a metre.
Truth: The Ten digit GPS co-ordinates give a location to the nearest metre but in practice I have found that about 25 metres is the most you can expect on a regular basis.
I have taken a GPS reading from a cairn in the morning and returned to the same cairn later in the day to find my GPS Receiver telling me its 20m to the left (or right) of its true location. In any event, when you get that close, the GPS can't quite make up its mind and the targeting arrow starts to rotate with the message 'Arriving (Destination)'.
Garmin's Owners Manual for the eTrex states:
The eTrex is accurate to within 15 metres without the Department of Defence imposed Selective Availability. Using differential techniques, the eTrex can be as accurate as 1-5 metres. The eTrex is accurate to within 100 metres under Selective Availability.
Another factor that will effect the accuracy of the GPS receiver is the geometry of the satellites in view of the GPS receiver. A poor geometry situation can provide less accurate position readings, and this especially applies to GPS altitude measurements. The altitude reading on the GPS unit can vary by +/- 450ft (137m) depending on the level of degradation being imposed under Selective Availability.
It is not uncommon to see the altitude continuously drift up and down when Selective Availability is being imposed.
This discrepancy is also due in part to the earth and the satellite orbits not being truly spherical so the distance from your GPS Receiver to the satellites is slightly different for each reading.
In most cases, except in very poor visibility, you'll be able to see the target from within 100m – so 25m accuracy is perfectly acceptable.
Myth: Walking and Hiking GPS Devices will not work if it is raining.
Truth: Walking and Hiking GPS Devices were originally developed for sailing - so they need to be (and are) waterproof.
A Walking and Hiking GPS Device works just as well if the day is wet or dry. It will take a dunking in a cold beck or hot coffee and still work fine. It doesn’t mind thick cloud cover, but it’s not too keen on trees (see below).
Windy weather however has a curious effect on the altimeter on some GPS Devices for Walking and Hiking.
Myth: GPS Devices for Walking and Hiking will not work indoors or in forests.
Truth: A Walking and Hiking GPS Device needs to be able to 'see' the sky and the satellites up there. It will not work well beneath a canopy of trees and will not work at all in thick forests.
Similarly it will not work indoors - though you can get a reading if you hold it near or out of the window (and you are not in a heavily built up area). Walking and Hiking GPS Devices do however work in a car.
Myth: A Walking and Hiking GPS Device affects the readings on your compass.
Truth: It will - so you must keep the two apart.
A Walking and Hiking GPS Device is best switched off and stowed away when using a compass. This will also help to save the batteries.
Incidentally, you get some pretty bizarre readings if you use a compass near a car too.
Myth: This article has been written by a map and compass loving GPS-a-phobe.
Truth: I always carry a Walking and Hiking GPS Device with me into the hills and use it regularly to confirm my position. On a couple of occasions I have had to input local co-ordinates from a go4awalk.com pdf in very thick weather in order to locate a summit. On each occasion I have found this a quick and easy task and the Walking and Hiking GPS Device led me straight to my intended target without incident.
There is no denying that a Walking and Hiking GPS Device might just save your life. Finding your current location is virtually instantaneous and a ten digit GPS co-ordinate given to the rescue services via a mobile phone would speed up search and rescue significantly.
Navigation by map and compass is fun, easy to accomplish and can be very satisfying - but in really tricky situations when I need that extra reassurance that I am where I think I am, I switch on the GPS and can be found peering at the screen.
*NB. Compass and map navigation is a basic skill that you must have if you’re going into the high hills, fells and mountains. If you don't have the skill - learn it. A Walking and Hiking GPS Device is not and never will be a sufficient substitute for basic skills. Click here for more information and some detailed tutorials on Grid References and Navigation Techniques
GPS Navigation Systems for Walking and Hiking - The Myths and Truths - Part 2