Rick and all,
�
Actually there is an issue with probably all of the CBC count centers.� For many years I was the "official" (volunteer) approver of all new CBC circles for Audubon.� This was back in the days when maps were on paper and determining center coordinates was challanging in most cases.� I had access to all the 7 1/2 minute topographic maps at work, so I would do my best to get them as accurate as possible.� But the problem was not one of accuracy, it was one of precision.� Audubon only wanted the coordinates to the nearest minute of latitude and longitude, so in most cases they were off by as much as a half mile or so even if they were completely accurate.� When they put the data on the web, they used those 'nearest minute' coordinates to calculate the decimal degrees. The decimal degrees were calculated to as many as 4 decimal places (remember 'significant digits?'), giving the impression of great precision.� But because they were based on the
original rounded minutes, they rarely pinpoint you at the actual center.� This is very obvious when the Annapolis, Bowie and Triadelphia circles are plotted.� We positioned the Bowie count to exactly touch the other two circles, but not overlap.� When you plot the three, there is overlap.� Also, the center of the Annapolis count is the south end of the rte 50 bidge over the�South River.� The coordinates at Audubon are .58 mi. WSW�of there. So�looking at the edge of a circle for what is in or out can be tricky.� Of course, it can be argued that a half mile is not a big deal, but many counts were positioned to capture specific areas at the edges.
�
Now that we have Google Earth and other such resources, it would probably be wise for count compilers to re-figure center coordinates to an accurate 4-decimal place figure and inform Audubon to correct them.� Audubon should also have a disclaimer about this and somehow�differentiate corrected centers from the "incorrect" ones.
�
Danny Bystrak
Bristol A A Co.
________________________________
From: Rick Hollis <xiboia...>
To: MdDC Birds <mdbirding...>
Sent: Tuesday, December 18, 2012 6:44 PM
Subject: [MDBirding] KLZ files [google earth] for count circles
The NAS has count circle files which are downloadable at�http://birds.audubon.org/faq/where-can-i-see-cbc-circles-map
http://www.nemesisbird.com/2012/12/mapping-the-christmas-bird-count/ has a discussion�
BUT there is a issue with some of the centers. The Iowa City Christmas Count Circle was off by 1.4 mile in the data release in 2011. �The files they released this year is even farther off, 1.67 miles.
I am not sure what the NAS chart options descried in the nemisisbird post above, gives the wrong center for our count.
Having said that, the Google Earth views are extraordinary -- far better than any old fashion maps. �If you locate your real center and draw your circle, you can find out whether bushes are in count circles -- the photos for our circle are within the past couple months. �My Mom's house in Balto has 2010, where as my Sis [Surgarloaf Circle] has 2011 images.
Rick Hollis
North Liberty IA & Arbutus MD--
--
|