Geocaching and graphing

I did a mini-unit with my 7th grade technology class this week using GPS devices. First we reviewed latitude and longitude and I went over how to use the devices. I have a set of 12 low end Magellan GPS units so the students worked in pairs. Then we went outside and I made sure everyone had signal and that the units were working properly. I then had the students walk around our parking lot and write down the seconds of the coordinates every 10 feet or so in this table. We only wrote down the seconds because it was a small enough area that the minutes and degrees never changed.

The next day the students typed the seconds into two columns in Excel and made a line graph. If they did a careful job the graphs turned out very realistic. If their graphs looked bad it was usually from one or two points being way off. We "fixed" the numbers by changing them to numbers nearby for a best fit, and the graphs looked much better. In the past I had students map out the perimeter of our school. This did not work as well because the building blocked signal from the satellites and we got inaccurate readings.

The third day (our last real day of class) I hide a couple of pieces of candy in 10-12 spots around the school grounds. I had students bring out a pencil, paper, clipboard, and their GPS. After everyone's device had a good signal I gave them one set of coordinates and they took off to find the loot. It is important to only give one set of coordinates at a time otherwise some students run ahead and find all of the caches before everyone else (previous years experience). After someone found one I would give everyone the next set of coordinates. The kids had fun and if I would have had more time it could be tied even more into graphing on the coordinate plane.

In previous years I have taken students on a "walking field trip" and we left school property to find some real caches in our neighborhood. That was a lot of fun also, but required me to get permission slips which I did not feel like dealing with this late in the year. Local caches are easy to find at http://www.geocaching.com/  Sign up for a free account and you can search for them. I also like to use this site http://confluence.org/ to show students how far apart degrees are and what confluence is.

One other mini discussion we have is how a GPS works. I ask them if they think a GPS sends a signal, receives signals, or both. Most of them think both, but actually they only receive a time stamp from satellites. Then the device uses the difference in time to compute distance. The distance from different satellites make intersecting circles of a Venn Diagram to narrow down the location. After a unit gets signals from at least four satellites it will track in 3D.

All in all my GPS unit was fun and students learned some real world math skills. Geocaching also encourages exercise through walking and biking. (my students were running to find the candy). If you can get some higher quality GPS units you can upload and download maps to use with them and study terrain and lots of other social studies topics. It was a great way to end the school year.