You know those Pocket Query files you get from Geocaching.com, or the files you can download directly from a cache page when you click on the "GPS eXchange File" button? Did you ever wonder what they are exactly? Well, we'll try to solve that little mystery here.
These GPS exchange files, or GPX files for short, are designed specifically for describing and transferring GPS data between software applications. They can be used to describe waypoint, tracks, and routes. Its tags store location, elevation, and time and can in this way be used to interchange data between GPS devices and software packages. Such computer programs allow you, for example, to view your track, project your track on satellite images (e.g. Google Earth), annotate maps, and tag photographs with the geolocation. The minimum properties for a GPX file are latitude and longitude for a single waypoint. All other variables are optional.
Go ahead and download a waypoint from a cache web site on Geocaching.com by clicking on the "GPS eXchange File" button:
Now open up the file in a text editor, such as Notepad. You should see various tags describing all the different aspects of the cache, including cache name, owner, date placed, type, terrain, and most importantly, latitude and longitude. Basically, the file contains all the information you would find on the cache page itself, but in a format that allows you to transfer that information to your GPS or to other software and web applications that can consume that information.
In these previous posts, we discussed some of the many things you can do with your GPX files, beyond just copying them to and from your GPS device. For example, you can open them in Google Earth for viewing waypoint locations, you can upload them to web sites such as GPS Visualizer and AnalyzeMyTrack to view your data in different ways. The possibilities are endless.
For more detailed information, see the this discussion on the Topografix web site.