What can I do with a GPS?


If you are a walker and you are thinking of buying a GPS then the important question must be "What can I do with it?".

There are a few good answers to that question and some not so good ones. The manufacturers and sellers also do their bit to cloud the issue. Indeed the supporting software produced by the manufacturers can readily justify a "What should I avoid doing with it?".

So, for what they are worth, here are my answers to the main questions.


Will it locate me when I am lost?

If mist and fog close in and the countryside lacks features, then getting home safely can be really difficult and drawn-out. If you are carrying both a GPS and the relevant Ordnance Survey map then you can locate yourself to within 6 metres.

Just knowing where you are is usually enough. However there are some other useful things a GPS can then do for you. You could look up the map references of some point or points that you need to pass by on your way home. Once you have keyed-in these to your GPS then you can use the "Go to" facility. Just start walking and the GPS will soon respond with messages like "Right 23°, Distance 2.1km" and then perhaps followed by something like "Left 2°, Distance 2.1km" as you respond by making a change of direction.

Anyone who has done this for real, using only a magnetic compass, will know just how hard it can be if your direct line has streams, bogs and cliffs scattered in your way. Boxing and multiple boxing can stretch the best navigator. However, with a GPS it is child's play. Just walk around the edge of the bog and ignore the GPS for the moment. Once you are safely past the bog you can move back on to the most direct course.


Will it tell me how long the walk was?

We have all tried pedometers. They work fairly well if you are on flat ground and keep to an even stride. But just try walking up and down steep paths with exposed tree roots on them and you may see your pedometer reporting three times the distance you have travelled. It has been counting every little step and stumble you make as if it was a normal stride!

Likewise, I have experienced walking slowly steadily and smoothly up a long incline of about 400m in length without my pedometer recording even one single pace! (It had failed to recognise any steps at all as I "flowed" along the path)

In contrast, a good GPS should be able come up with an accurate distance on any type of terrain. [But do see the information on this website about odometer errors produced by Garmin software]


Will it let me record a walk?

Nearly all newer models of GPS will record a complete track and will have a built-in connector to let you transfer the readings to a computer. [A "Track" is a point by point record tracing your movements]

OK, so this does mean you have still got some organising to do, but it is not too onerous for anyone who likes gadgets. You need to buy and fit a suitable connection lead, you need to download suitable software from the Internet and you need to own a printer. From that you will be able to plot the track so accurately that you will sometimes be able to tell which pavement you walked on for sections done on a road!

The plot could take one of two formats. The simpler is to print it on a sheet of paper or a sheet of clear plastic. This will give you a very accurate shape of your route drawn accurately to the scale used. Depending on the software you use, you may be able to superimpose either an OS Grid over your trace or latitude and longitude lines. Also, most software could put a North Pointer Arrow on the print.

The second format, which is currently only available with Gartrip software, begins with scanning-in a map. You calibrate your scan by stating the coordinates of two map corners. You can then print a copy of your map with the track overlaid on it. [In most countries the map manufacturers would be legally entitled to charge a royalty for this!]


Will I be able to pass Tracks or Waypoints to a friend?

By using the software referenced above (or similar), you can get the information into your computer. Assuming your friend has all the same equipment that you are using, you can then send them the files on disk or as an E-mail attachment. They will be able to load the files into their GPS and march along your track simply by following an arrow showing on their GPS screen.

I think this is easily the best use of a handheld GPS.


Can it record Altitudes?

Caution! GPS units will determine altitude. The values obtained are independent of air pressure but are a little inaccurate.

A few of the more expensive GPS models use an internal aneroid {air pressure} altimeter and display the results from that. These units are accurate to about 5m vertically provided they have been set against a known height in the last hour or so. They are helpful for serious mountain navigation in cloud, provided you know and understand how their readings change with the weather.

It is essential for accurate work to set any aneroid altimeter shortly before using it. I can show you a trace where our "altitude" changed nearly as much during our lunch stop as on the rest of that Leicestershire walk - the weather was changing!

(There is more information available on another page of this site)


Can it pinpoint a location?

They all do this very well, provided that you like four-letter names for places. [Such recorded values are referred to as "Waypoints"]

Just press a button and then either accept the label (LM01, LM02 etc) or edit the label to CAR, LAKE, TENT etc. You can store this waypoint so perhaps you could return to it later. Alternatively you can display its coordinates as an OS Ref. or as Latitude and Longitude: you can then tell the museum exactly where you found the Roman Chariot or whatever.


Using with digital maps

A new and rapidly growing area for GPS units is their use with digital maps. This is really helpful. One can download a walk track straight into a map and study the surroundings of the walk on the computer screen and perhaps edit the track.

Also one can plan walks by clicking along footpaths with the mouse. Distances and elevations are instant and painless and the final track can be downloaded to the GPS and used to follow round the walk. UTM or OS map references can be taken from the map simply by pointing to the location with the mouse pointer.

I think the future will be digital, once the practice of over-pricing of digital maps is abandoned.


Anything else?

Yes, lots! For example you can get your current speed from most units. They will offer you a value for your maximum speed too. However, bearing in mind that it is calculated over a short time period and that GPS units show random plus and minus errors, you may find they tell you that you have exceeded Linford Christie's maximum speed by a factor of two.

Just don't base your choice of GPS model on the number of these extra facilities!


Some other things you could do
...but don't bother telling me about them!

Both of the main GPS manufacturers would be pleased to sell you a CD full of data, which you can download via a computer into certain GPS models. You will then be able to locate your nearest motorway service area or tourist information office ....and you can see stylised roads joining them. This can help you avoid being run over by a car.

If you accidentally bought the wrong CD you will even be able to locate lots of lighthouses and marker buoys. Good if some of your walks involve swimming across an estuary.

Indeed it seems that none of the GPS manufacturers are very interested in providing extra software that is useful to walkers. If you want useful software then you are reliant on enthusiasts. Happily, some of these enthusiast-written programs like Gartrip are first-rate by any standards.


And, finally...

The commonest question I have been asked by friends and acquaintances is "Does a GPS measure distances horizontally or along the slope of hillsides?". Maybe a written answer here would be a good idea.

The short answer to the question is that I do not really know. It is up to individual software or firmware writers. However I have always assumed that the norm would be to calculate distances between the 3-dimensional points determined by the GPS. If you don't do it this way then you will end up with some total nonsense in calculating the bigger distances because the Earth's surface is not 2-dimensional

For most purposes the error in question is small. I have just picked up my calculator and done some calculations on the Tour du Mont Blanc: a classic walk which would be regarded as "steeply up and down". The distance I have taken as 172km and the total ascent as 10943m. The difference in length between the "flat" and the "sloping" distance comes out at 0.2%. In contrast to that figure the 6% typical error introduced by Garmin's well-meaning attempts to eliminate spurious points from the odometer calculation is thirty times greater!