Now that it is easy to gather tracks and waypoints on a smartphone and map them in a GIS, it provides a good opportunity to remind students about the importance of being critical of and paying attention to data. I recently went on a walk around a local reservoir and used the Motion X GPS app on my iPhone to collect my track and a few waypoints. I emailed the data to myself and added the GPX file to ArcGIS Online so I could map and examine the track. I made my results public and made it visible below to feature some teachable moments.
Zoom in and examine my track and its attributes. How many times did I walk around the reservoir, and in what direction? What, then, is the line that extends from the reservoir 630 meters to the northwest? When I first turned on the smartphone and began my track, the GPS in the phone did not have enough information to plot my true position. Therefore, the positions plotted were nearby, but not exactly where I was walking until later. Examine the track and its attributes to determine how long I had been walking before the positions become accurate.
These “zingers” or inaccuracies often occur with tracks recorded on a smartphone, and on a standard GPS receiver as well. These results reinforce what we’ve long held as a “best practice”—to wait at your starting point as long as you can after starting your GPS or your Smartphone’s GPS app to ensure the most accurate positions possible on the data you will gather.
After the first 10 minutes, I was quite happy with the accuracy of Motion X GPS, within 1 to 2 meters as compared to the imagery in ArcGIS Online. Using ArcGIS Online you can clearly see each of my three laps around the reservoir. You can even see my attempt to write something in the parking lot using my smartphone using GPS drawing techniques, explained in this video I filmed. Although my letters should have been larger for increased clarity and avoid bumping up against the spatial accuracy of the GPS, I was still pleased with this portion of the experiment.
How might you use GPS apps on smartphones and ArcGIS Online to teach the principles and skills of accuracy, precision, GPS, and critical thinking?
-Joseph Kerski, Esri Education Manager