Where is the Coordinate Systems folder, and where are the projection files at ArcGIS for Desktop 10.1 and 10.2.x?

Answer

Note:
This article applies to only ArcGIS for Desktop versions 10.1, 10.2, 10.2.1, and 10.2.2. For more information on the location of the Coordinate Systems folder in ArcGIS for Desktop 10.3 and later, please review How To: Acquire projection files in the Coordinate Systems folder in ArcGIS for Desktop 10.3 and later

ArcGIS for Desktop now supports over 5,000 geographic, projected and vertical coordinate systems. Before ArcGIS 10.1, coordinate systems were included in the installation directory as .prj files in a Coordinate Systems folder. Installing the .prj files required a significant portion of the time taken up by the software installation process.

Each projection file is only a few hundred bytes when opened in a text editor, but because the information in the PRJ file must be stored in a block, with specific configuration, storage for one file requires four kilobytes for storage. Multiplying that by about 5,100 files, and the text projection files require about 20 MB for storage or installation.

To improve the installation experience and simplify localization support, the files are no longer included in the installation package. Instead, a virtual directory structure is built directly from the coordinate system data.

Commonly used coordinate systems can be exported to a Favorites folder. The physical location of this folder is the Application Data\ESRI\Desktop10.1\ArcMap\Coordinate Systems folder in the Windows profile directory.

Note:
The Coordinate Systems folder does not exist in the directory above until a projection is added to 'Favorites'. This path changes with each version.  For example, at version 10.2.x the folder location is:

C:\Users\<user>\AppData\Roaming\ESRI\Desktop10.2\ArcMap\Coordinate Systems

Custom .prj files can also be copied into this folder for use in ArcGIS. The Favorites directory can be accessed in ArcMap when setting the coordinate system of an ArcMap data frame on the View > Data Frame Properties menu, Coordinate System tab.

The coordinate systems in the Favorites directory are also available in ArcToolbox when using the Define Projection tool or the Project tool.