Talk:Geographic coordinate system

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[edit] Geocentric latitude vs true latitude

Is there an explanation of the difference between geocentric latitude and true latitude somewhere in Wikipedia? --Begemotv2718 23:52, 24 August 2005 (UTC)

See: Types of latitude. ~Kaimbridge~ 20:07, 4 November 2005 (UTC)

[edit] Only lat/long is mentioned

This article needs a lot of work. Why is the title "Geographic Coordinate System" when only lat/long is mentioned? What is the relevance of the diagram on the right? (Obviously that's rhetorical - I mean: what does it show?) Also, the whole section on lat/long is pretty incomprehensible. It should also probably mention that different meridians were in common use until the 20th century... Finally, the first sentence is wrong: a geographic co-ordinate system need not express *every* location on the earth - or indeed *any* location. Rolypole 21:23, 16 January 2007 (UTC)


[edit] Hexadecimal earthgrid

Match 213 added a long section which proposed a hexadecimal earthgrid. I am reverting this section because it violates official Widipedia policy which prohibits new ideas. It can be included only if those ideas have been published in some peer-reviewed journal, which must be cited. — Joe Kress 06:00, 14 November 2005 (UTC)


Hi Joe Kress, it was me as SP Match 213 (user contribuations) who introduced the paragraphe "The proposed hexadecimal geographic coordinate system".
I always think that this (not so new) scientific work is encyclopedia worthy. But at the moment I don't have the time to discuss and to argue on this topo.

I know you very well as a competent and sincere editor in Wikipedia. Therefore I don't resent you, that you have – for the moment – deleted this chapter.
As soon as I'll have more time, I'll come back to this topo. Interim, I invite you to follow the related discussions at the Talk:Fairway Rock Island page.

Have a good day, -- Paul Martin 11:37, 23 November 2005 (UTC)

[edit] Unsourced?

It looks pretty sourced (and common-sensical) to me. Why the 'unsourced' tag?Guinnog 21:44, 18 February 2006 (UTC)

[edit] decimal div

"Decimal division is now the most common and standard.": division?

"By combining these two angles, the horizontal position of any location on Earth can be specified.": at this point please hammer home that in some countries, if one doesn't add a third, datum, even more important than elevation, rescue crews could easily be sent somewhere a kilometer away.

Of course there is just as good a chance that rescue crews get their datums mixed up too anyways, or never thought about them.

Hammer it home here even though datums are mentioned below it.

--jidanni 2/06

[edit] in wikipedia

see Wikipedia:WikiProject Geographical coordinates.

It would help if the article talked about how the cooridinate system in wikipedia was used, since every page with cooridinates points to this page...
~ender 2007-09-09 13:26:PM MST
That is not possible given the Wikipedia guideline to avoid self-references to Wikipedia or to any Wikipedia project such as geographical coordinates. — Joe Kress 06:17, 10 September 2007 (UTC)
But I believe it does allow for disambiguation links at the beginning of the article. I added such a link to this article. Dbiel (Talk) 02:37, 6 November 2007 (UTC)
I've seen a template something like {{selfref}} for wrapping around such selfreferences. Maybe it's mentioned in WP:ASR. (SEWilco 02:48, 6 November 2007 (UTC))

[edit] Baltimore

Why is the example town Baltimore? Seems completely arbitrary to me. +Hexagon1 (t) 00:16, 11 November 2007 (UTC)

I don't know why Baltimore was chosen. Seems like a good choice to me; it's far from the origin (Greenwich), easily identifiable on many maps, and the nearby coastline helps during confirmation between maps of various styles. (SEWilco 15:53, 12 November 2007 (UTC))
Still arbitrary, is there no other widely used geographical beacon in the world but Greenwich? +Hexagon1 (t) 04:37, 16 November 2007 (UTC)

[edit] Spring Cleaning

For such an prominent article, this one seems tired and in need of a good cleanup and revision. Is anyone going to object if- I remove the purple prose, remove the irrelevant links zB Greeks. Correct the facts in line with "A guide to coordinate systems in Great Britain v1.7 Oct 2007", explain datums and Helmert transformations, make Baltimore grid reference consistent with Baltimore article, explain relevance of time, and accuracy constraints? ClemRutter (talk) 16:18, 13 April 2008 (UTC)

Be my guest, although I have no idea what "irrelevant links zB Greeks" means. I don't think that Helmert transformations would be appropriate here because it has its own article, unless you can reduce its complexity substantially. — Joe Kress (talk) 04:28, 14 April 2008 (UTC)

Here is the first draft- Greeks are in a footnote, Baltimore has gone and I have structured it so that the casual user has a few paragraphs which discuss all GCS, then the heavier geography and maths follows. I want to replace the diagram that says little, and look at why the map uses Eckert VI which is difficult to explain. What do you think.ClemRutter (talk) 16:43, 15 April 2008 (UTC)

I started to copyedit your first draft but immediately ran into significant problems, so I thought I'd give you a chance to correct them first. One signifcant point is that latitude is not measured via the center of the Earth, but is the angle between a line perpendicular to the surface of the ellipsoid (either a geoid or a datum) and the equatorial plane—the line usually does not pass through the center of the Earth, except for rarely used geocentric coordinates. The other problem relates to your introduction of the three basic methods of specifying coordinates, DMS, DM, and DD. Arabic numerals never replaced Roman numerals in geographic coordinate systems—they replace Greek numerals, which, in the system used by Ptolemy, were a place value system regularly using six sexagesimal places (a precision of 2×10-11), at least in astronomy. In geography, if he only used degrees, minutes and seconds (he may have only used DM), he did so simply because of the roughness of his data, not because he couldn't use more precision.
Within each sexagesimal place Arabic numerals have been used ever since they were introduced into Western Europe about 1200, from 0 to 59 for each place. These places were named minutes, seconds, thirds, fourths, fifths, sixths, etc. Astronomers were still regularly using six sexagesimal places as recently as 1740 when Jacques Cassini did so. He was a noted geographer as well, using triangulation to measure an arc of the French meridian, so it would be interesting to see what notation he used geographically. Thus the change to our present mixed sexagesimal/decimal system must be relatively recent. Astronomy now uses a mixed system (at least for right ascension) just like other time and angles do, including geographic coordinates: minutes and seconds plus decimals, or minutes plus decimals, or only decimals. — Joe Kress (talk) 21:05, 15 April 2008 (UTC)
Cassini used d ' " (degrees, minutes, seconds) throughout his book wherein he presented his triangulation, De la grandeur et de la figure de terre (1720), for example page 135. But on page 236 he used thirds, e.g. 2d 12' 9" 30'", as well as a simple fraction after seconds, e.g. 51d 2' 25" ½. On page 286 are several thirds. I still find at least one 'third' in 1829 in Nouvelles tables astronomiques et hydrographiques by V. Bagay on page vi. — Joe Kress (talk) 06:20, 16 April 2008 (UTC)

Fantastic response. I know I read all this once- but didn't buy the books, at the libraries closing down sale! All this needs to be recorded- to me the question is where. I'll tell you my thinking.

  • This article is accessed by a link from every geotag on Wiki, so it is incredibly important that the first two or so pages are kept focussed on what this reader needs to know.
  • From the point of view of 'Dr. Joe Public' or a doctoral student accessing the article, they must understand the 4 myths (see OSGB ref) so they don't waste time assuming their primary source map from say (1910) will have the same lat/long as their GPS/Wikipage.
  • After that, the article flies in two directions, the nature of geodesic transformations, and the relation between this and the History of mathematical thought and numerical representation.
  • I am torn between the desire to include everything and the desire to keep on subject

So I suggest that we need a section on the History of GCS, which gives a synopsis of the fields development, and a full article called something like the History of GCS. In the same way the Helmert is obliquely described, then a link given. In the History Case I think it should be For more information see.... tagged. I readily concede, that my latitude definition is an approximation, but so early on in the article nothing was defined (geoid, planes of equal gravitation potential) and I wanted to keep it concise and not take the reader down a mental rabbit hole, but to keep focussed. I see the problem and would be inclined to use a footnote to help clarify. I haven't wanted to introduce Greek numbers as for outside the world of Maths, Greek numbers are not a current concept so they obfuscate rather than illuminate. I am acutely aware of the number of new concepts one can hold in one's head at one time. There are a few thought's- sorry it's only brief- life get's in the way of Wiki! ClemRutter (talk) 09:45, 16 April 2008 (UTC)

There are other history articles distinct from a modern treatment of the same subject, so your suggested split is not new. I'll let you decide how you want to lead the reader into the subject, but I do feel that the fact that latitude is not via the center of Earth is more important than a footnote. Indeed, upon reading A guide to coordinate systems in Great BritainPDF (718KB), I find that this is included within Myth 1, that their is no single coordinate system. See latitude for its many types. A compromise might be to say near or about the center of Earth with a statement to see a later section where the distinction is explained in more detail. Before the prolate vs oblate spheroid arguments of the 18th century, Earth was assumed to be spherical so latitude was via its center at that time. Jacques Cassini was on the losing side, believing that Earth was a prolate spheroid. It is also a myth that Earth was ever believed to be flat, at least in Europe. See Flat Earth. I see no real need to discuss the history of geographical coordinates here—my explanation was to point out that the distinction between DMS, DM, and DD was not due to ancient history, but is quite modern. I do not know of any reason for that distinction other than the personal style of each writer and his relative importance in the last few centuries. — Joe Kress (talk) 22:37, 16 April 2008 (UTC)
Geodesy for the LaymanPDF (3.42MB) or Geodesy for the Layman (html) by the United States Defense Mapping Agency (now the National Geospatial-Intelligence Agency) is also a good source of info, especially for GPS. — Joe Kress (talk) 23:14, 16 April 2008 (UTC)
I have made a couple of holding changes and added the pdf link. Doing a bit more thinking. ClemRutter (talk) 09:22, 17 April 2008 (UTC)

[edit] Graticule

Redirected here from Graticule, trying to find out what that was and where it came from. Graticules are not even mentioned on the page. It seems odd to search for a topic, then be referred to a page that makes no mention of it. (Maybe I missed the section on graticules? Apologies if that's the case.) --Thomas B♘talk 04:41, 21 May 2008 (UTC)

I assume you came here after reading the latest XKCD blag post? I did. So, I think a "graticule" is a grid square on the coordinate system, at some level of precision. -- Phyzome is Tim McCormack 13:54, 21 May 2008 (UTC)
Yes it is——it got lost in an HTML remark, during an edit last month. It has now been restored and augmented. P=) ~Kaimbridge~17:49, 21 May 2008 (UTC)

[edit] US or British spelling

As I understand it, "centre" is British (as against "center" in American), but neighboring is American (as against neighbouring in British). I really don't mind whether the article uses American or British English, but it should be consistent. I am changing it to British spelling, I can't think of a good reason to choose one over the other though but I'm British myself so I claim first mover advantage. Also "centre" pre-dates "neighboring" in the edit history. — PhilHibbs | talk 14:44, 29 May 2008 (UTC)