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What Projection does ArcGIS use as its geographic projection

January 05 2009 | 0 comments
Categories: ArcGIS Methods, Map Data

A favor, please. Can you find out what projection ArcGIS uses as its geographic projection? Is it the simple cylindrical projection?

Mapping Center Answer:

As of ArcGIS version 9.2, there is no longer a "geographic projection" in ArcGIS. The "geographic projection" was a troublesome concept from its inception in that it explicitly had no definition. In some ways it was a product of its time when there was a great deal of data in existence that lacked coordinate system information. Times have changed, and the vast majority of datasets have coordinate systems defined. The following online help topic explains the details of how ArcMap currently works:

http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?id=204&pid=197&topicname=Specifying_a_coordinate_system

That sets up the circumstance of "No Projection", for a data frame in ArcMap that does not have its coordinate system property set.

The other concept that is useful is "Unknown Coordinate System" which applies to those datasets that lack a coordinate system definition. The following is an online help topic that discusses that situation:

http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?id=90&pid=86&topicname=Identifying_an_unknown_coordinate_system

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