updated: plotting a christmas bird count circle

December 24, 2011

in Field work, Science

This is Christmas Bird Count (CBC) season, the roughly three-week period at the end of each year where teams of determined folks do single-day bird surveys of established 15-mile diameter circles (history here). Typically, participants are given a photocopy of a road map with the count circle drawn on it with that high-tech instrument, a compass. This can make for some imprecise boundaries, to be sure, and it is important to stay within the count circle in order to improve the scientific validity of potential analyses.

In 2005, I posted a tutorial on how to create a very precise circle in Google Earth that would show the exact circle boundaries and allow you to zoom in, check for promising habitats, save or print the whole circle or just a portion, and all the other cool crap Google Earth lets you do.

Since then, more people have created mash-ups and tools for Google Earth, and I’ve found one that is easier than the method in my previous post. For starters, it’s online and will put your circle on a Google map on the same page where you input your parameters. You can format the boundary line and fill various thicknesses and colors. And you can export your circle into a KLM file that will open in Google Earth, so you can save it, revise it, and enjoy all the Googly-goodness.

  1. Go to the Free Map Tools radius around a point page.
  2. Pick your radius. For a CBC, the radius is 7.5 miles. It will work for any type of circle, of course.
  3. You can zoom in on the map at the top of the page to pick the center of your circle, but for the sake of precision, input the official center by using decimal lat/long. The best way to get this data is to head to the newly revamped National Audubon CBC page, and query the historical results for data on the count circle you are interested in. Use the options to find the count you want — the years you look at really don’t matter. You just want to click on “Make a table” so you can look at the coordinates Audubon has of the count circle center. They’ll be right at the top of the table, in decimal degrees (clickable, actually, to Google Maps, but the map will only show the center point, not the circle itself). These are the coordinates you plug into the Free Map Tools page. If in North America, make sure you include the negative sign in the longitude, or else your circle will end up on the other side of the world. If you only have your center point in degrees-minutes-seconds, you can go to this page and covert it to decimal degrees.
  4. Choose your aesthetically pleasing options.
  5. Click on “Draw radius” next to where you entered your lat/long data.
  6. Presto. Your circle is on the map.
  7. To see your circle in Google Earth, scroll down to the “Google Earth KML Output” section, and click the “Generate KML” button. In the space below, a link will appear to the KML file. Click it.
  8. If you have Google Earth installed on your computer, you can choose to open the file right then and there. Or you can save the file and open it in Google Earth later.

There are other options on the page for viewing, saving, and/or linking to your circle as well. Happy bird counting!




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