[texbirds] Re: Count Circle and CBC centers
- From: David Sarkozi <david@xxxxxxxxxxx>
- To: jjones4fwas@xxxxxxxxx
- Date: Sat, 23 Nov 2013 07:48:45 -0600
Jim a consideration in a paper map count circle is a circle on a map is
only a circle when the map projection is a great circle projection centered
on the center of the count circle. I did some checking with a gps that gave
me the distance to a landmark set on the physical description of the count
circle. In this case the center was something I could walk right up to so I
know my center was 100% accurate. I found even though I has a USGS map with
the radius drawn properly, the gps showed that by edges were off by as much
as a quarter mile. In my case it made very little difference, but there are
cases where something areas are counted at the very edge of a circle and it
could be a big deal.
I know the Bolivar Penn Count circle coordinates on the NAS websites are
incorrect, they show most of the circle in the Gulf of mexico, when only
about a mile of the Gulf is actually in the circle. When I took over
compiling that count, sent in a correction but it doesn't appear to
actually have "stuck" I have matched up the physical description with
landmarks on the edges of the circle that Bill Graber gave me that he used
to draw the original map and they match up well, but I chalk the error in
the coordinates to maps 50 years ago just weren't as easy to use as Google
Earth is today.
On Thu, Nov 21, 2013 at 4:06 PM, JimJones-FWAS <jjones4fwas@xxxxxxxxx>wrote:
> I felt that I needed to address two issues I have with some of the comments
> about this App and the CBC data shown on the National Audubon Society
> website.
> I do not have the App so it may in fact be a wonderful thing to behold. But
> one of the replies on TexBirds said if you don't like where your circle is,
> the APP allows you to submit a request to change it. I sure hope that the
> App developers contact the local compilers before doing any changes.
> Otherwise, the historical census in a well-established CBC becomes useless.
> My second issue is with the CBC map available on the NAS website. If the
> App
> and the NAS data are interlinked, be aware of one glaring error with the
> NAS
> map.
> I take part in two local CBCs in Fort Worth, the Fort Worth CBC and Village
> Creek Drying Beds CBC. I looked at the NAS CBC map and saw that the drawn
> circles did not extend out as far as the Topo map we've used for many
> years.
> I measured both of the local circles on the NAS website and discovered they
> are drawn at 12.6 miles in diameter!?! I also looked at and measured five
> other CBC circles in north Texas. All are shown as 12.6 miles in diameter.
> A
> CBC circle is to be 15-miles in diameter.
> If you use the NAS map or the App (if it has the same fault in its design),
> be aware that you are losing over a full mile of the outer-radius in your
> circle area.
> I agree with Bush's comment: know your area.
> I would add: if needed, go to the library and get a survey map that
> includes
> your circle and draw the 15-mile circle onto it. If the library can't make
> copies for you, write down the map number and hit the internet. I collected
> these types of maps for many years. As recently as 2003, I purchased them
> from various stores and government agencies. Stores that specialize in
> hiking and other serious outdoor activities usually have local maps
> available.
>
> Jim Jones
> Bedford, TX
>
>
>
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--
David Sarkozi
Houston, TX
(713) 412-4409 twitter ID dsarkozi
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