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Using a GPS to help with navigationGPS devices are becoming much more commonly used as a navigational aid on the hills. Although many walkers prefer to escape from technology when out in the wilds and prefer to rely on their well-honed map and compass techniques, others are increasingly using GPS as a additional aid to safety. We've written this article to outline how the different ways a GPS can be used to help you find your way in the hills. The article covers: Using your GPS to give your current position See also our brief articles on: How to program a route into your GPS Using a GPS to give your current positionThe most basic and perhaps useful function of a GPS is that it can give you your current position with a high degree of accuracy. The grid reference reading (most GPS devices can give you an OS grid reference) means that you can see where you are on your map – and as long as you can read the map, you'll then be able to work out on what bearing you should be heading. In the most trying conditions keeping track of your current location using only a map and compass is tricky, though a skill well worth learning. It involves counting your paces as you walk along a compass bearing so you can estimate how far you have come. To do it accurately, you need to know how many paces you take to cover a set distance, allowing for different types of terrain and steepness of slopes. Modern 'H'-class GPS receivers can give your current position to around 5 meters accuracy or less – greater than anyone is likely to achieve on a hill using only traditional techniques. A basic GPS, such as a Garmin eTrex H, will give you the grid reference to check against your map; these are the cheapest devices and can be used on their own. The most advanced devices, such as Satmap, can actually hold map images themselves and so actually show your location on an on-screen map, with controls you can pan around; to do this, you have to buy the mapping too, which can be expensive. In between are devices that can hold 'Topo' maps – basic maps with perhaps contours and roads but lacking the detail of an OS or Harvey Map. Using a GPS to aim for a particular point Satmap Active 10 - showing OS map The next step is to get your GPS to help tell you in which direction to go, rather than just where you are now. If you know your current position, everyone in the hills should know how to take and walk along a bearing using a compass. But there are situations where keeping to a bearing can be difficult. If visibility is reasonable you can pick out an object on the horizon and aim for that. But if visibility is very poor then the rocks or other features you can aim for will not be far away, and keeping on a bearing becomes more difficult. This is compounded if the route also crosses difficult terrain – having to divert around broken crags or awkward ground make it easy to keep straying further and further from the intended line. In these circumstances, it can help to program into the GPS the grid reference for the point you are next aiming for, e.g. a summit, or a bealach that is key to a safe route off the hill. The GPS has the advantage over a compass that it constantly adjusts for your current location, so if you are forced off course by the terrain the GPS will constantly adjust the bearing you need to take to reach your target. The only problem is that entering points like this is the field can be very fiddly and mistakes are easy to make. If you want to take advantage of a GPS in this way, it is better to pre-load your target waypoints or route. Using a GPS with a pre-loaded routeFor details on how to get a route loaded onto your GPS, see the next section.  Garmin eTrex H - in map mode Having your intended route pre-loaded into your GPS makes it perhaps the most useful aid of all. To get the line of the loaded route to be shown you need to choose to 'follow' it on most devices. Most GPS's then have a screen that simply tells you in what direction you should walk to reach the next waypoint on your route. This is used by geocachers to find their hidden stashes, but isn't particularly useful on a hillwalk as the terrain may mean you do want to divert from the loaded route to some extent – and the GPS won't be giving you any help with this.. Instead we've found the best way to use a GPS with a pre-loaded route - whether you have a GPS that shows full OS mapping or just tracklines and waypoints - is to have the display showing the map screen when following the route. The intended line will then be shown on the screen (it looks like a road on an eTrex H, and a coloured line on a Satmap), and you can see where you are in relation to it at all times. This means your GPS won't be forcing you to exactly follow the programmed route, but always can help you understand at a glance where you are compared to what you had originally planned. When used in conjunction with a map this is huge aid to navigation in many circumstances. For instance, when a route crosses a plateau, running close to the edge of a cliff (that may well have a dangerous snow cornice), traditional navigation in poorer visibility would involve 'boxing' – deliberately aiming ninety degrees from the edge until a safe distance from it is reached before walking on the correct bearing set back from the edge, and then correcting once beyond the danger. In the same circumstances if you have a GPS that already has the route along the very edge of the cliffs programmed in correctly, you can use the loaded route to show the cliffs location and use your GPS display to walk parallel to the edge at a safe distance of a few hundred metres. Another example is the common error made with a map and compass when leaving a summit towards two almost parallel ridges. Without a GPS you may not realise you've joined the wrong ridge until far down, whilst with a pre-programmed route you'll be able to see that you have diverted away from the intended ridge. Whilst a GPS won't make you safe if you can't read a map (see link below) there's no doubt that it can improve your safety. GPS Navigation - Introduction |
