"what is a '.gpx' file?"
This is what GeePeeEx Editor edits (Gee Pee Ex - geddit?).
 
"GPX, or GPS eXchange Format is an XML schema designed for transferring GPS data between software applications. It can be used to describe waypoints, tracks, and routes. (According to Wikipedia)
 
Very impressive, but, what does that mean?
In the Garmin® StreetPilot® and Nüvi® ranges, '.gpx' files are used to transfer "Waypoint" or "Point-of-Interest" data back and forth from the SatNav to your PC. These relatively low cost units do not allow detail Route Planning on the PC - it is all handled in the SatNav itself. The Zümo™ range does allow for Route Planning and records your 'Track' as well. (This functionality has also been added to the new Nüvi® 7xx range).

The unit stores your 'Favourites' in \Garmin\GPX\Current.gpx. These are accessed by pressing the "Favourites" button. To store a new one, press the current position indicator (i.e Car,Truck, Motorcycle or whatever symbol you are using).
 
You can also store information for addresses you have looked up, and Points of Interest (POI's) you found in the map data itself. The '.gpx' specification allows for a wide variety of information to be stored, but when used in this mode, the Garmin® unit uses a much cut down version - presumably for speed of access. You can have a maximum of 500 Favourites - though this figure may vary with model and firmware version.
 
Points of Interest
Convenient as these are, a more powerful mechanism is the 'Custom POI' location. Favourites (or non-favourites, such as Speed Cameras!) can be stored in this location and the full range of data can be stored, including Proximity Alert information. As well as full address and phone number details, you can also store an associated image and a description page (which can use a subset of html markup to format it to your liking).
 
These 'Custom POI's' cannot be edited on the SatNav itself - which is both an advantage and a disadvantage. They are best used for less dynamic data, as opposed to 'Favourites' (and its automagically filled-in cousin 'Recently Found" locations').
 
Garmin's POI Loader
It should be noted, that these 'Custom Poi's' are not read directly from a '.gpx' file - they have to be compiled into Garmin's '.gpi' format, using their 'POI Loader' program (which is available free of charge from their web-site). POI Loader accepts two forms of input.
 
  1. .CSV (Comma Separated Values) files - these allow a maximum of 4 fields (Longitude, Latitude, Name and a comment field). Speed alert information is denoted by using the format @speed in the name field, e.g Gatso@40. This format is very easy to understand (and edit), but only allows for a limited amount of information to be conveyed.'
  2. .GPX' files - Using this format, the full range of options that the unit understands can be used.
 
So - show me a '.gpx' file then - I'm ready to create one
Unfortunately, one look at a '.gpx' file can be enough to put most people off:-
 
<?xml version="1.0" encoding="Windows-1252" standalone="no" ?>
<gpx xmlns="http://www.topografix.com/GPX/1/1" creator="Human" version="1.1"
xmlns:xsi=http://www.w3.org/2001/XMLSchema-instance
xsi:schemaLocation="http://www.topografix.com/GPX/1/1/http://www.topografix.com
/GPX/1/1/gpx.xsd">

<wpt lat="59.921055008" lon="-103.054223107">
<ele>122.863281</ele>
<time>2007-05-16T11:59:06Z</time>
<name>Could be anywhere</name>
<sym>Skull and Crossbones</sym>
</wpt>
</gpx>
 
That is just a simple example.Click here for a real one.
 
Now '.gpx' is a form of XML - and it is simply not designed to be read (or written) by humans (I got that line from the Microsoft website). I have formatted the sample above for clarity, but it would be perfectly valid, if written all on one long line. As well as being very picky -it's cAsE senSitiVE for starters - there is another issue:
 
You may have created a '.gpx' file that passes general XML validation and maybe even specific GPX validation, but still is unacceptable to POI Loader. 
 
POI Loader does not have many error messages in its repertoire. It'll tell you it doesn't like it ... and it's then down to guesswork as to why not. It says:
 
"The file xxxx is invalid, Do you want to continue?"
 
After you've received that message for the two-dozenth time - the answer might well be "No!"
 
Garmin® make this statement in their POI Loader Help file:-
 
"These features require advanced skill and technical knowledge and are only recommended for advanced users"

 
This is just one of the reasons you need GeePeeEx Editor
 now anyone can create Garmin custom gpx files!