GPS Help

GPS receivers are becoming an increasingly popular route finding accessory, and work in a similar way to satellite navigation in cars. They are a useful back-up to a map and compass, in showing your precise location, distance and speed travelled, and what direction to go to reach the next point on a pre-plotted route, or to retrace your steps. More advanced models have larger screens, which can display all this against a backdrop of Ordnance Survey maps.

At the bottom of each route page is a button to download a GPS file. Right-click on this and select ‘Save link as’ or ‘Save target as’. The files are in a GPX (GPS eXchange) format because this can be read by most different models and makes of GPS receiver, and opened by most mapping software, including Google Earth (Plus version only), Memory Map, Anquet Maps and Tracklogs (Tracklogs is used to generate the GPX files for my routes). Load the downloaded GPX file into your GPS device. For details of how to do this for your GPS or mapping software, please refer to its manual.

Each GPX-format file consists of ‘trackpoints’ and ‘waypoints’:

A Track consists of an ordered list of Trackpoints and defines a detailed track (called a ‘tracklog’). The trackpoints along a track are defined every few metres or when the path deviates significantly from a predicted position. A track may contain several hundred or even thousands of trackpoints. Tracks define the detailed path between 2 waypoints, whilst a Route only shows the straight line path between 2 waypoints.

Each Waypoint is a turning point along the route with a defined coordinate and a description of the route to be taken to the next waypoint. Waypoints are sequentially numbered. Sometimes waypoints are refered to as Points of Interest (POIs). A Route is an ordered lists of waypoints, and GPS devices can ‘lead’ you around a route, from one waypoint to the next. A Route consists of 10 to 50 waypoints.

The GPX files are supplied in good faith, and it is up to the user to exercise discretion and caution when using them. Between each waypoint is a connecting straight line indicating the shortest route a ‘bird would fly’ between the waypoints, which misses out many small twists and turns of the path (which are defined by the trackpoints). The connecting line only implies that two waypoints are sequential. Each of the waypoints is located on the path, but the connecting line may veer off by up to 20 metres and so it is NOT SAFE OR POSSIBLE TO PRECISELY FOLLOW THE GPS LINE ON THE GROUND.

It appears that different GPS devices interpret the GPX files of my routes differently. My Nokia N8 (mobile phone with GPS built in) has an application Viewranger on it. This actually claims that the GPX files do not contain a route at all, but contain one track and several POIs (it interprets waypoints as POIs). However, Viewranger allows a track to be converted to a route, automatically inserting waypoints. Then it leads you around the route, from one waypoint to the next. Along the way, the POIs can be viewed to provide more information about the route.

To ensure that these downloads are as useful as possible I would appreciate feedback, or reports of any problems in using it, via the Contact Us page.