[APG Public List] [APG Members] place names

Stephen Danko stephen at stephendanko.com
Tue Oct 26 00:29:46 MDT 2010


GPS coordinates can be specified so that they represent either a large general 
area or a spot the size of a pinpoint.  It's all in how many significant figures 
one lists in the coordinates.

The number of significant figures refers to the number of numerals in the 
coordinate.  37.79507, -122.40280 has 7 significant figures in the N-S 
coordinate (the first number) and 8 significant figures in the E-W coordinate 
(the second number).  This is the location of the Transamerica Pyramid in San 
Francisco.  Actually, it is the location of a part of the Transamerica Pyramid.  
This coordinate has so many significant figures that it points to a 
very accurate location on the earth.  If the coordinate is written as 37.8, 
-122.4, the area described becomes much larger and includes anything between 
37.75 to 37.84, -122.35 to -122.44.  Written as 37.8, -122.4, the coordinates 
don't accurately specify the Transamerica Pyramid, but instead specify about 
half of San Francisco.

Note that 37.8, -122.4 is not the same as 37.8000, -122.4000.  The first set of 
coordinates gives a general location (the eastern half of San Francisco) and the 
second set gives a very specific location (the corner of Vallejo and Front 
Streets in San Francisco).

The latitude longitude system we use today is based on a prime meridian through 
Greenwich, England.  Historically, different places used different prime 
meridians (including prime meridians in Paris, Washington, D.C., and Rio de 
Janeiro).  For genealogical purposes, all historic systems can be ignored and we 
can use today's system with a prime meridian through Greenwich because, as Larry 
pointed out, our goal in using latitude longitude coordinates is to specify 
where a place is today, using today's system.  Using GPS coordinates, Nicole (in 
a different thread) would have immediately been able to find out where 
Grossendorf, Germany was, and she would have immediately been able to see that 
the present name of the place is Władysławowo, Poland.

True latitude/longitude coordinates are not exactly the same as GPS 
coordinates.  This is because GPS uses the International Reference 
Meridian which is 102.5 meters east of the Prime Meridian through the Royal 
Observatory in Greenwich.  Don't worry about the reason for this difference.  
Google Earth used GPS coordinates instead of true latitude longitude 
coordinates, presumably so that GPS systems will match up with Google Earth.

In summary, GPS coordinates can be used to describe a very specific point on the 
earth or a very general area of the earth depending on the number of significant 
figures in the coordinates.

Kind regards,
Stephen J. Danko
http://www.stephendanko.com/




________________________________
From: Connie Sheets <clsheets1 at yahoo.com>
To: apgpubliclist at apgen.org; apgmembersonlylist at apgen.org
Sent: Mon, October 25, 2010 4:33:55 PM
Subject: Re: [APG Members] [APG Public List] place names

I must admit to only a general knowledge about, and frequent lack of attention 
to, GPS coordinates.  I have been operating under the assumption they describe a 
specific point on the earth, not a large area like a rural US township of 36 
square miles.

I can comprehend how I might want to visit the crossroads approximately one mile 
southeast of a very small village in Northwest Missouri where my great-great 
grandfather's house once stood, obtain the GPS coordinates, and record them for 
posterity with a photograph I have of the house.  I also understand how GPS 
coordinates are useful for locating cemeteries, graves within cemeteries, and 
other landmarks.

However, if all I know about an ancestor's location is a rural township or 
county, I would be concerned that I was promoting inaccuracy if I arbitrarily 
chose (and yes, it would be arbitrary) the center of the township or county.

I will continue to use standard historical place names, with a reference to the 
modern place name when necessary, for the foreseeable future.

Connie Sheets
Arizona
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