Can anyone recommend a good reference or tutorial that explains the principles of spatial references, projections, and coordinate systems?

We are a small team of programmers working with GIS technology, and we often get snagged when working with data in different SRS/CS because we don't understand the concepts.

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Personally, for the cliff's notes I find the ESRI ArcGIS desktop software help system useful, and and also the ESRI book Understanding Map Projections, its first 30 pages are not unlike a short textbook, followed by ~70 pages of appendix on individual projections, their uses, strengths, weaknesses, etc.

From these, you'll quickly understand all the pieces of a complete SR - spheroid + datum + meridian + unit of measure => GCS; and projection + parameters + unit of measure + GCS => PCS.

For all the math, try the classic USGS Professional Paper 1395 by John P. Synder - Map Projections - A Working Manual. You might find a PDF somewhere if you google it.

Finally, take a look at the 'documentation' links at the bottom of the page for the Proj.4 library.

And as a DB of spatial references, I tend to refer to http://www.spatialreference.org/ or another ESRI list provided as part of the docs for their ArcGIS Server REST API.

Hope that helps.

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Answering a question about the difference between a projection and a datum, Bill Huber links to his article in the Directions Magazine where he gives introductory explanations of georeferencing, datums, spheroids, and the like.

As short and concise as it can be!


I think Carlos Furuti's tutorial is a really good resource.


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The PostGIS in action book has a great chapter, 6 - Spatial reference system considerations, on these subjects, although it is (of course) a bit targeted at PostGIS use. Well worth checking out.


The OGP have lots of useful information on geodesy, try:


They also have a GIGS (Geospatial Integrity of GeoScience Software) program, more info here and also via OGP:



I just ran across NOAA's "What is a Datum".

They seem to have more info on vertical datums than other sites I've seen.

(I guess data is no longer the plural form of datum.)

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Here's one for Arc that goes through several scenarios using vector data: http://blog.geographyforever.org/2013/03/25/working-with-spatial-reference-systems-in-arcgis/

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