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I hear people complain:

my biggest gripe with google spatial apis is that they hide the fact that latitude/longitude is not a universal coord system

My question is Is latitude / longitude a universal coordinate system? What are the implications if it is not?

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Can you provide a link to where you saw this? –  PolyGeo Mar 3 at 11:14
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Could you please explain what you think "universal" might mean? I can imagine senses in which the answer is yes and other senses in which the answer is no. –  whuber Mar 3 at 15:30
    
And what does "they hide the fact that latitude/longitude is not a universal coord system" mean? –  martin f Mar 4 at 2:11

5 Answers 5

up vote 12 down vote accepted

It depends on what you mean by 'Universal Coordinate System'. If you wonder whether most Professionals understand Latitude and longitude, well in that case it is pretty much universally understood.

But if you ask, whether it is used by everyone, then the answer is a resounding, No. There are many reasons why people use projected coordinate systems instead of a Geographic Coordinate system, such as:

  • Pre GPS, it was far easier to find the location with more accuracy in a local Projected Coordinate system, than a Global Geocentric Coordinate System. This was not only due to variety of control points available in a Local system, but also because it is computational easy.
  • It's far easier to calculate distances and bearings in a projected coordinate system.
  • Web Mercator has become the defacto projection for web mapping, because it is a projection which is locally conformal, i.e. it preserves the shapes and directions at large scales.
  • And lets not even get into legacy and statutory reasons for using projected systems.

Amongst those people who use Geographic systems, there may not be universal agreement about what reference system to use. There are different datums that one could use, as well as different prime meridians that could be used. This comes into play, if you are searching for long lost treasure, or if you go to the Greenwich Observatory with a GPS and wonder why you are not at 0 longitude

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I am struggling to figure out why precision has anything to do it... –  mkennedy Mar 3 at 17:00
    
@mkennedy the precision especially comes into play when you are dealing with projected coordinate systems. When you flatten out a predominantly spherical surface (the earth) onto a flat projected surface, you end up either having to stretch some spots and/or compress others to square it up. Different systems compress/stretch different places differently. A projected coordinate system for Mexico for example, probably wouldn't work well for Greenland as there could be all sorts of distortion. Therefore you would get greater precision if you used a localized projected system for Greenland... –  John Mar 3 at 18:20
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@user2856159, I would call that accuracy or distortion, not precision ( = number of significant digits). –  mkennedy Mar 3 at 18:25
    
@mkennedy I agree as far as the technical terminology goes, but my assumption would be that is how precision was intended in the above answer. If you believe it is a significant issue that could cause confusion for others reading the answer, you should consider using the edit button to propose a correction to the answer that seems, otherwise, rather on target. –  John Mar 3 at 18:28
    
@mkennedy, yes you are right. I should have used the word accuracy. –  Devdatta Tengshe Mar 3 at 18:42

The bunch of different lat/lon datums we have is a relict of the first surveying done on national basis. These had their limits on the borders (mainland or overseas colonies), and noone thought of putting a universal CRS at that time. As a consequence, getting lat/lon coordinates always needs a question about the datum they are in. While local projected coordinates can easily be separated from their extent, it is much more difficult in lat/lon systems.

Tectonic moves are yet another reason against using universal lat/lon coordinates.

The plates have already moved since WGS84 was established. That's why the Europeans put up their ETRS for surveying restricted to their tectonic plate. As a consequence, WGS84 was ammended by time frames to fit to ETRS. You can think of that as a datum on a time axis rather than locally restricted like the old datums were.

Up to now, it has not yet come to the attention of many GIS people, but those living on the edges (like on Hawaii) think different about this.

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I agree with the essence of Devdatta Tengshe's answer, except that I believe the main reason for the common use of plane (projected) coordinates over geographic (lat-lon) coordinates is one of computational convenience.

It was and still is very difficult for people or surveyors to do basic CoGo (coordinate geometry) calculations on the sphere (using geographic coords) as compared to doing the same with projected (plane) coordinates.

True, if we do use geographic coordinates as though they were simple plane coordinates, and conduct simple plane computations, then the results are less and less accurate the further away we away from the equator. However, since the use of geographic coordinates pre-dated the invention of cartesian coordinates by thousands of years, the use of such simple (but inaccurate) CoGo methods would not have been possible until cartesian coordinates were invented.

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I've updated my answer to clarify what I meant by more accurate. It is partly dependent on being computationally less intensive, but also depends on having control/reference points in the local coordinate system. –  Devdatta Tengshe Mar 4 at 3:15

Would it be facetious of me to point out that it hasn't been literally universal since Galileo disproved the Ptolemaic system?..

Ok, ok.. Lat Long is the most widely used global system but by no means the only one.

http://kartoweb.itc.nl/geometrics/coordinate%20systems/coordsys.html

As to why people would gripe about Google Earth... projections wouldn't be my first reason but it apparently causes some frustration :

http://alastaira.wordpress.com/2011/01/23/the-google-maps-bing-maps-spherical-mercator-projection/

But I suppose from this quote they mean that Google automatically re-projects lots of different data onto Lat Long and doesn't really make clear it has done so. That seems a bit unfair, they will tell you if you ask :

https://support.google.com/earth/answer/148110?hl=en

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Not that this adds depth to the conversation, but the timing is right and it is interesting. I received this the other day from a co-worker; bringing up a similar conversation.

All of you which participated in this question might find reading this somewhat-serious, somewhat-humorous suggestion worthwhile. It's a quick read and suggests that when all else fails, use WGS 84 lat long.

http://calvinmetcalf.com/post/59491281511/map-projections-are-fundamentally-broken

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More project references here: radicalcartography.net/?projectionref –  hawkeye Mar 4 at 21:15
    
@hawkeye Thank you, I will check it out! –  MapHound Mar 4 at 21:47

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