Choosing a GPS suitable for hiking

Before you to choosing a suitable GPS for your hiking needs, it is important to have a reasonable understanding of what is on offer along with how they work.

There are several components that need to be looked at. There is the GPS receiver (or antenna) itself, which plays an important part. Then there is the portion of the system which uses the received information to estimate where the device is located on an internal map.

Then there are the various capabilities for route planning and recording, which vary from unit to unit. Finally, the display portion of each solution type can vary considerably, from limited location information to full color three dimensional maps of the immediate surroundings and advised route.

How it Works

The actual principal of GPS is very easy to appreciate, since it produces similar results to traditional "triangulation" although GPS does not use angles. If one imagines an orienteer needing to locate themselves on a map, they first need to be able to find at least three points that they recognize in the real world, which allows them to pinpoint their location on the map.

They can then measure, using a compass, the azimuth (This is the direction of a celestial object, measured clockwise around the observer's horizon from north) that would be needed to take them from the point on the map to their current position. A line is then drawn from each of the three points, and where the three lines meet is where they are on the map.

Translating this into the GPS world, we can replace the known points with satellites, and the azimuth with time taken for a signal to travel from each of the known points to the GPS receiver. This enables the system to work out roughly where it is located, it is where the circles representing the distance from the satellite, calculated on the basis of the travel time of the signal, intersect.

Of course, this requires that the GPS locator has the same coordinated time as the satellites, which have atomic clocks on board. To do this, it cross checks the intersection of the three circles with a fourth circle, which it acquires from another satellite.

If the four circles no longer intersect at the same point, then the GPS system knows that there is an error in it's clock, and can adjust it by finding one common value (one second, half a second and so on) that can be applied to the three initial signals which would cause the circles to intersect in the same place.

Behind the scenes, there are also many complex calculations taking place which enable the system to compensate for atmospheric distortion of the signals, and so forth, but the principle remains the same.

Updates & Mapping

When choosing a GPS, it is important to bear in mind that each type will be updated in a different way. For example, dedicated in-vehicle units tend to be updated via a CD, which has to be purchased from the road map data supplier.

Those which are attached to a PDA, as well as most handheld dedicated GPS devices, are usually updated via a PC. They also need maps, but said maps can usually be acquired at a much lower price than the dedicated branded ones needed for other systems.

Being able to update the device easily and at a reasonable cost is a very important part of the decision process; unlike other consumer devices that you purchase, the cost of ownership of a GPS unit is proportional to its usefulness.

The less you spend on maintaining it, the less useful it becomes since the road networks are always changing. This is perhaps less important for devices aimed at hiking and orienteering, but could be a factor in deciding whether a multi-function device is better than one dedicated to a specific use.

Specific software vendors have solutions for preparing maps which can be uploaded into the GPS unit. For example, many are based around the mapsource system which permits users to define their own maps, perhaps scanned from a real one, in order to get the most out of their GPS.

Accuracy & Portability

If accuracy is paramount, then it is also important to choose a unit that is equipped with a WAAS (Wide Area Augmentation System) capability assuming it is available in the region the unit is being used.

This is a satellite service which provides additional correction information to the GPS receiver which enables it in order to increase its accuracy.

WAAS equipped devices might be especially useful for road users and those involved in either door-to-door selling, or providing a service which requires them to be able to pinpoint their position right down to a few feet.

On the other hand, it is useless to purchase a WAAS capable system if the service is not available in the area in which the device is to be used.

If portability is a key part of the decision process, then it will usually be a trade-off against accuracy, whether that accuracy stems from poor GPS signal acquisition, or less powerful software coupled with a less detailed map.

Important features to consider when selecting GPS for hiking:

The features needed on a GPS can be a personal thing however when hiking is involved the features needed are a generally more extensive than for other uses such vehicle navigation for example. Listed below are the important features recommend for GPS when it comes to hiking. These do not include the standard features present on All receivers.

1. It is best to have a "Map" screen rather than a numerical lon/lat position fix, this makes it much easier to see where you are relative to reference waypoints.

2. "Built in Maps" make it a lot easier when it comes to orientation and estimating distance to nearest roads etc.

3. "Map memory" We recommend at least 20 megs for a mapping GPS although you can get by with as little as 1.4 megs if you are only using local topo maps on your hikes.

5. "Route capability" it is best to have at least 20 routes

6. "Waypoints": get one that can store at least 500.

7. "Multiple Datum capability" make sure all the datums you will want to use are included in the GPS you select.

8. "Screen size and readability" Screen size and your ability to read it are important especially when it comes to viewing fine detail. B&W screens are fine for hiking. Many color screens are hard to read in direct sunlight, however the more advanced "Trans Reflective Color screens" are an exception as they are easy to read in bright sunlight.

9. "Bearing to next waypoint" features are essential when it comes to hiking.

10. "12 channel parallel receiver system" provide the best reception in difficult terrain and tree cover.

11. Make sure the unit is compact and light to carry.

12. The unit should be rated "submersible" making it waterproof.

13. "Long life batteries" avoid the need to carry so many batteries. However it is always advisable to carry at least one replacement battery.

14. "External amplified antenna" although not essential, they handy to have if you are going to encounter heavy tree cover or difficult terrain conditions involving multi paths etc

15. Ability to upload topo maps is also a useful feature to consider although not essential.

The Choice

In the end, the choice is reasonably straightforward - if price is a deciding factor, then buy the most expensive one you can afford which fits your needs.

Try to think about the following:

Portability

Features

Mapping and Updating

Environmental Features

Portability is affected by weight and size, as well as the antenna. This could have an effect on the features that the device offers - clearly if the screen is tiny, and the whole unit is about the size of a cell phone, then some advanced features will not be fitted.

The mapping and updating capabilities are also important. Should it be able to accept any old map from a PC, or is it enough that the unit is replaced after 5 years? Technology moves almost as fast as the roads are updated, so this could be an option.

Finally, are there any specific environmental options that are needed, such as waterproofing, rugged shock-proof design, or other features that make one device more attractive than another?

Answering these questions will help determine what type of GPS receiver that is right for you, and at the right price.

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