Mapping your trail
Mapping a trail these days using a GPS receiver is very straightforward. You can create a very basic trail map by simply walking the trail with GPS on, recording a "track log" along the way.
As they say, "The devil is in the details." Some important considerations you should be aware of:
- What does the terrain along your trail look like? Narrow valleys, heavy tree cover, box canyons and similar situations will degrade your GPS accuracy and affect results. There are solutions to this using professional grade GPS equipment and editing tools.
- At what scale will your finished trail map be rendered? If you will depict your map results zoomed in at a low scale and very small area, any inaccuracies in your trail recording will be readily apparent. Again, using professional grade GPS equipment and editing tools will help.
- How will the finished map be used? You may wish to include elevation and even time stamp information. Elevation can be used to generate a profile of your trail and rate difficulty. Time stamp information can be used to create a fly over of the trail, or show average time to trail highlights.
- Are you "Tech Savvy"? GPS receivers are fairly easy to use. The basic editing tools for removing errors in your GPS track log are also straightforward. But, they're not for everyone. If in doubt, we're happy to do as much as you want to move the process along.
Recording a Track Log
- When you first arrive at the trail, simply turn the GPS receiver on and give it time to acquire satellites. Pay close attention to Estimated Position Error (EPE) or Dilution of Precision (DOP) as measures of GPS accuracy. Look for an EPE below 30' (if possible, but different mfrs calculate EPE differently) before starting your hike. DOP should be below 2.0.
- When you're ready to start walking and recording your track log, DO THIS FIRST: Check your track log settings and CLEAR the track log memory. That will ensure that your first track point is at the trailhead. Depending on whether your are on foot or on a bike, you may find that a recording every 5-10 seconds or every 1-3 seconds gives you the best results. Don't use distance intervals for your recording; they will miss or distort switchbacks.
- Now simply walk the trail, keeping your GPS receiver in a place where it will continue to have best possible reception. In your hand where you can watch GPS status is best. On the outside and top of your backpack is also good if you need free hands for pictures, etc. If you stop for a break, either pause your recording or leave it sitting in one place on the trail and you can edit out any scatter in post-processing.
- When you reach the end of the trail, don't forget to save it. Many Garmin receivers will attempt to refine you track log when you save, and you will lose a lot of detail in the saved file. For the best detail you'll want to shut off the GPS receiver and back in the office retrieve the "active log" file showing all data points recorded.
Editing a Track Log
- Back in the office you'll want to download the track log to your PC for viewing and editing. Many GPS manufacturers (shame on you, Garmin) use proprietary formats for their track log data, in which case you'll need to use their software to download the file (ex., MapSource).
- The end-target format you'll want is .GPX. There are many tools out there for converting the various proprietary formats to .GPX. We recommend that you use GPSBabel.
- Once you have the file in .GPX format you'll want to view the resulting file and edit out (a) any scatter, especially at places where you may have stopped for a time, or (b) any overshoot of turns where the position points extend beyond the turn in the trail. We recommend that you use GPXEditor to clean up your track log files.
- Save your finished file, giving it a good filename with a date, in case you plan to do some more edits.
Finishing your Trail Map
- Your final steps will depend on how you will distribute your map information: online as a map, online as a .GPX file for others to use on their GPS receive, or as a printed map.
- If you're creating an online map image or a printed map, consider using Global Mapper to view your finished track log over a variety of background images. You can make some additional edits within Global Mapper and create your scale and legend.
- If you intend to publish your .GPX file for others to use, get the word out! There are many good places to share your trail data, including: