Comments on: What equation should I use to calculate the number of miles in a degree of longitude for a given latitude?
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Comments on Ask MetaFilter post What equation should I use to calculate the number of miles in a degree of longitude for a given latitude?Tue, 19 Aug 2008 05:06:11 -0800Tue, 19 Aug 2008 05:06:11 -0800en-ushttp://blogs.law.harvard.edu/tech/rss60Question: What equation should I use to calculate the number of miles in a degree of longitude for a given latitude?
http://ask.metafilter.com/99539/What-equation-should-I-use-to-calculate-the-number-of-miles-in-a-degree-of-longitude-for-a-given-latitude
What equation can I use to calculate the number of miles in a degree of longitude for a given latitude? <br /><br /> Because the number of miles in a degree of longitude becomes zero at the poles, it's safe to say that as we travel north (anywhere in the USA, anyways) the number of miles in a degree of longitude shrinks...post:ask.metafilter.com,2008:site.99539Tue, 19 Aug 2008 04:56:22 -0800GlendalelongitudelatititudecalculationequationBy: cardboard
http://ask.metafilter.com/99539/What-equation-should-I-use-to-calculate-the-number-of-miles-in-a-degree-of-longitude-for-a-given-latitude#1448155
The diameter (proportional to circumference) of the longitudinal circle varies with the cosine of latitude, so it would be equal to 60 nautical miles, the length of a degree at the equator, times the cosine of the latitude.comment:ask.metafilter.com,2008:site.99539-1448155Tue, 19 Aug 2008 05:06:11 -0800cardboardBy: le morte de bea arthur
http://ask.metafilter.com/99539/What-equation-should-I-use-to-calculate-the-number-of-miles-in-a-degree-of-longitude-for-a-given-latitude#1448159
On land (statute miles, as opposed to nautical) you're looking at more like 68.7 * cos(latitude)comment:ask.metafilter.com,2008:site.99539-1448159Tue, 19 Aug 2008 05:10:31 -0800le morte de bea arthurBy: miasma
http://ask.metafilter.com/99539/What-equation-should-I-use-to-calculate-the-number-of-miles-in-a-degree-of-longitude-for-a-given-latitude#1448162
If you're looking for an approximation, you can use <a href="http://en.wikipedia.org/wiki/Great-circle_distance">Great Circle Distance</a>, which assumes that the earth is a sphere.<br>
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If you want some quick approximations, its 69 miles at the equator, 0 at the pole, and about 49 miles at 45 degree latitude.<br>
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If you want something precise, try Google Maps or Google Earth with its distance calculation. This should take into account WGS84 or something similar<br>
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If you're looking for code, try the <a href="http://jscience.org/">JScience</a> or <a href="http://www.sedris.org/">Sedris SDK</a>.comment:ask.metafilter.com,2008:site.99539-1448162Tue, 19 Aug 2008 05:12:43 -0800miasmaBy: miasma
http://ask.metafilter.com/99539/What-equation-should-I-use-to-calculate-the-number-of-miles-in-a-degree-of-longitude-for-a-given-latitude#1448163
Or if you want a quick approximations, google for "geodesic distance" ala http://www.movable-type.co.uk/scripts/latlong-vincenty.htmlcomment:ask.metafilter.com,2008:site.99539-1448163Tue, 19 Aug 2008 05:15:44 -0800miasmaBy: vacapinta
http://ask.metafilter.com/99539/What-equation-should-I-use-to-calculate-the-number-of-miles-in-a-degree-of-longitude-for-a-given-latitude#1448165
This is basic trigonometry. I'll show you how.<br>
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If you imagine the Earth is a sphere, then what is the radius of a circle of constant latitude?<br>
Draw a triangle to any point on that circle from the center of the Earth.<br>
The hypotenus is just the radius of the Earth. We know the angle - its the latitude.<br>
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Remember SOHCAHTOA?<br>
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Well, Cosine(latitude)=Adjacent/Hypotenus<br>
Adjacent is the radius of the latitude circle.<br>
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So, Adjacent=Cos(L)/R<br>
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You want to know the ratio of that circle to the circle at the equator, right?<br>
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Ratio=Cos(L)/Cos(0)=Cos(L)<br>
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So, at Latitude L, the length of a degree of longitude is Cos(L) times the length at the equator.comment:ask.metafilter.com,2008:site.99539-1448165Tue, 19 Aug 2008 05:16:02 -0800vacapintaBy: brianogilvie
http://ask.metafilter.com/99539/What-equation-should-I-use-to-calculate-the-number-of-miles-in-a-degree-of-longitude-for-a-given-latitude#1448168
Um, folks, cardboard gave the correct answer at first. No need to keep answering, unless to do as vacapinta did and explain the reasoning behind the answer.comment:ask.metafilter.com,2008:site.99539-1448168Tue, 19 Aug 2008 05:20:00 -0800brianogilvieBy: lukemeister
http://ask.metafilter.com/99539/What-equation-should-I-use-to-calculate-the-number-of-miles-in-a-degree-of-longitude-for-a-given-latitude#1448181
The circumference of the Earth is roughly 25,000 miles, so 1 degree of longitude at the equator is approximately 25,000 miles/360 degrees = 69.4 miles. (It's 69.2 miles if you use the more exact value, 24,901.55 miles, for the circumference.) <br>
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69 miles*cos(latitude) should be close enough for government work.comment:ask.metafilter.com,2008:site.99539-1448181Tue, 19 Aug 2008 05:43:44 -0800lukemeisterBy: exphysicist345
http://ask.metafilter.com/99539/What-equation-should-I-use-to-calculate-the-number-of-miles-in-a-degree-of-longitude-for-a-given-latitude#1449159
Please do not look up "geodesic distance" or "great circle distance" or find the distance in google earth. They have nothing to do with the question you asked. The correct answer is quite simple, has been given several times, and involves the cosine of the latitude.comment:ask.metafilter.com,2008:site.99539-1449159Tue, 19 Aug 2008 18:51:19 -0800exphysicist345By: jpdoane
http://ask.metafilter.com/99539/What-equation-should-I-use-to-calculate-the-number-of-miles-in-a-degree-of-longitude-for-a-given-latitude#1449763
Well, because the earth is not perfectly spherical, the above answer is only approximate.<br>
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<a href="http://en.wikipedia.org/wiki/Geographic_coordinate_system#Expressing_latitude_and_longitude_as_linear_units">Here </a>is a more accurate formula, which models the earth as an ellipsoid, rather than a sphere.<br>
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(Ultimately, there is no *exact* formula, because the earth is not an *exact* geometric shape)comment:ask.metafilter.com,2008:site.99539-1449763Wed, 20 Aug 2008 08:36:34 -0800jpdoane