using google earth to map christmas count circles

December 23, 2005

in Science

There is a new and improved version of this post here!

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.

Now CBC participants can superimpose an exact, properly-sized circle on a lovely hybrid satellite image/road map, know exactly where the count circle boundaries are, zoom in, check for promising habitats, and save or print the whole circle or just a portion.  Here’s how to do it, using Google Earth, which must be installed on your computer.

  1. In Google Earth, find the center of the count circle, and add a placemark (Control-N).  Make sure the placemark is in exactly the right spot by zooming in.  (The default placemark is a dorky large pushpin.  You can change it by clicking on the pushpin to the right of the placemark name in the dialog box.)  If you are using Google Earth with locations marked in decimal degrees, skip to step 6.  If you are using it with locations in degrees, minutes, and seconds, perform steps 2 through 5.
  2. Right click on the placemark, and choose Edit.
  3. In the Edit box, click on Advanced.
  4. Click on the Location tab, and copy down the latitude and longitude of the placemark/count circle center.  Close the Edit box.
  5. Now open your browser and go to this page on the Federal Communications Commission web site to convert your latitude and longitude (which is in degrees, minutes, and seconds) into decimal degrees. When entering the data in the green box, make sure the last box includes the decimal point given in Google Earth (i.e., 26.71 or 7.57).  Results appear on the next page.  Copy them down.
  6. Go to the KML Circle Generator and enter your decimal degrees. Here in North America, you have to make sure your longitude is preceded by a negative sign. Else, you end up somewhere in China.
  7. In the radius box, enter 12070.08, the conversion for a 15-mile diameter circle.
  8. The result will be a hyperlink.  Click it, and the dialog box should ask if you’d like it to open in Google Earth.
  9. Voila! Google Earth opens and you have a lovely red CBC circle centered around your placemark.  How cool is that?

Major hat tip to Blended Technologies for most of these instructions.


P.M.Bryant December 23, 2005 at 10:02 am

Thanks for the tip. Now I only need to find the opportunity to take part. It's not looking good for this year. Next year maybe? Whenever it is, it will be my first, and I am looking forward to it.

Lanny December 23, 2005 at 10:10 pm

Is that viola a flower or a musical instrument?

Lanny December 23, 2005 at 10:13 pm

Arrgh! The blog removed my "ducking and running" comment.

Jim Maloney December 23, 2005 at 11:17 pm

You might mention that GoogleEarth does not work with Mac computers (at this time) according to the GEarth website.

TroutGrrrl December 24, 2005 at 12:42 pm

Very very cool!

Pamela December 27, 2005 at 9:03 pm

Participated in the Belleville,ON CBC today–don't know how our count area was determined–not a circle but a squiggly looking shape on the map, one of, I believe, 10 sections the count area is divided into. I just followed orders. Highlights: 5 eastern bluebirds, 2 northern shrikes.

Jack Harlan November 10, 2006 at 1:00 pm

One can skip the steps of converting the lat/lon from deg/min/sec format to
decimal degrees by simply going, in
GEarth, to "Tools", "Options", "View" and
making sure you've checked the "Lat/lon"
button "Degrees" instead of "Degrees,

Bill Schmoker November 13, 2006 at 1:29 pm

Thanks for the great directions to do this. I've taken it one step farther, by dividing up the CBC I compile (Boulder, CO) into territories using the Add Polygon tool in Google Earth Plus. Details and screen shots here:

Thanks again & keep up the great work. -Bill

paul January 5, 2008 at 11:09 pm

Thanks for posting this: it was a great help. Trying to work out what places are within a given walkable/bikeable circle is a good thing, and this made it easy.

David December 10, 2008 at 2:34 pm

Here is the perfect solution, as long as it will remain around for us:


Nuthatch December 10, 2008 at 7:03 pm

Ooooh. That's cool. Thanks David!

For folks wanting to give that link a try, just inputting a decimal lat/long didn't work, you'll have to move the map so the crosshair is the center of your circle; when you input the radius in km, the correct number is 12.07008.

Comments on this entry are closed.

Previous post:

Next post: