GIS Tool: GPS Units

Being the Magical Mapper, I’m often asked about GPS units and why I don’t just use the built-in GPS unit in my smartphone to collect GIS data. While consumer GPS technology is getting better every day, most GIS analysis requires a little bit better locational accuracy. Regular GPS units like recreational GPS units or the chips in smartphones can get you within a few meters if conditions are excellent (estimates are 16 ft. under wide-open skies), but you typically don’t know the accuracy of each point captured (so you know what types of mapping or analysis are appropriate to conduct with your collected data). This article gives a good overview of GPS accuracies, and this blog post explains it in a bit more detail.

Basically, this means that if you’re trying to map a location of an outfall that you’ve tested for poop (er… fecal coliform), and want to get back to it (and not mix it up with other ones in the vicinity), you need a mapping-grade GPS unit and shouldn’t trust your phone (unless you want to make awesome drawings to carry with you).

Mapping-grade GPS units can have accuracies ranging from a few centimeters to within a meter of the actual feature you’re collecting and store the accuracies for each point. With new rules being applied and apps being developed, it’s conceivable that I may use a smartphone one day to collect data…

Most GIS Professionals are still using mapping-grade GPS units, like the yellow Trimble units you may have seen (there are many brands out there but this is the one I’m most familiar with). There are a lot of new versions now that are just a little puck sized device that connects to a tablet or phone via Bluetooth. With with apps such as Fulcrum, or Esri’s Collector or Survey123, you can create a much more user-friendly map or form to use with the GPS unit but still get the accuracy you want. If you don’t care about locational accuracy so much, or if you already have your feature mapped but need to add additional information (or return to take another sample), you can still use these apps to collect data.

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