Today’s blog serves two purposes: (1) inform readers what’s going on in my research world and (2) an educational piece sharing some of my trials and tribulations with ArcGIS this week.
Right now we are preparing to deploy a glider up in the Gulf of Alaska, near Homer, in the US Navy’s Gulf of Alaska Temporary Maritime Activities Area. The glider’s acoustic system samples at 194 kHz allowing us to listen for vocalizations up to 97 kHz, which covers almost all cetacean species in the area, except porpoises which vocalize at really high frequencies (>150 kHz, we recorded them with a different glider though!).
I won’t be actually going out to deploy it or piloting this glider – we are collaborating with some folks from the University of Washington – but I am responsible for putting together the glider’s track and coming up with track points that are 5 km apart so we can set our ideal path for the glider. Why am I responsible for this, you ask? Well because I took an introductory GIS (Geographic Information System) course so….this becomes my job.
For those of you that have worked with GIS, you understand there is a STEEP learning curve. It may be one of the least intuitive programs on the planet. But, it is incredibly powerful for not only making maps but for spatial analyses too, so I am super happy to have learned even a tiny bit about it and get to learn more every week.
Well I’ve made these maps before for Guam and Hawaii, so Gulf of Alaska, easy peasy! I’m finally starting to remember how to make the track from the initial way points, then turning the track into 5 km spaced points. But, news flash! The earth is round. And measuring things at higher latitudes gets weird/complicated/annoying/inaccurate/etc.
So this week (really the last two days) I taught myself about projections in ArcGIS. Projections are basically trying to show our round, 3D Earth in 2D. At the equator this isn’t so bad, but up (and down) by the poles things can become really distorted.
Take this image of the US for example. Depending on what projection you use, it looks slightly different! And those differences are more pronounced the further north you get. So by the time you get to Alaska…well, you’ve got to do something about it.
Fortunately, lots of people have made hundreds of projections for different areas and different spatial scales that reduce distortion, either in area, distance, angles, etc.
So then all I had to do was find the one I needed (this took much research and trial and error), then redo all my mapping/measuring/GPS coordinate extracting steps on a correctly projected map. You know, once you make sure all parts of your map are in the same projection, that the data frame has the right projection, and that you saved it every 5 seconds in case it crashed. Once I got past the frustration, I ended up pretty proud of myself, and now I learned my lesson for next time: only work in areas near the equator.
Want to know what projection I used? Of course you do. The lovely Alaska Albers Equal Area Conic! Sorry I can’t share a picture of the pretty map…I’m not sure I should show you where our glider will be I don’t want anyone going up to Alaska and stealing it.