Proxy files

When a raster is used in ArcGIS, and auxiliary information (such as statistics, histograms, and pyramids) cannot be found inside the raster or in an associated auxiliary file, ArcGIS will build and store it. Normally, it is stored inside the raster itself if the format allows it, or it can be written to auxiliary files next to the raster. When a raster is marked with read-only permissions, or when the folder it is located in is marked as read-only, these auxiliary files are subsequently written to a different writable location and are known as proxy files.

What files can be contained in the proxy location?

Three types of files can be written to the proxy location:

• Proxy Unrestricted Access Image (UAI) files point to the read-only raster dataset and use a uniquely named prefix that incorporates the path of the data plus a UAI suffix. This is the file that points to the original read-only data. This naming convention is used to avoid overwrites of AUX files when more than one raster from different folders is similarly named.
• Proxy AUX files are the main auxiliary files associated with the UAI file. This file follows the UAI file prefix-naming convention but has an AUX or AUX.XML suffix. Like normal AUX files, the proxy AUX files store additional information, created by ArcGIS, and cannot be stored inside or beside the raster because of the raster's (or its folder's) read-only permissions.
• Proxy OVR or RRD files hold the pyramid data as normal OVR or RRD files, but they are stored in the proxy location because of the raster's (or its folder's) read-only permissions. The proxy location will never contain original raster data.

Where is the proxy location?

The raster proxy files are placed in the RasterProxies folder located in each user's temporary directory. This location will vary per machine. If it is deemed preferable or necessary to change this location, a registry setting is provided for this purpose.

To control the location where proxy files are written, use the ArcMap Advanced Settings utility (AdvancedArcMapSettings.exe), which can be found in the Utilities folder of the ArcGIS for Desktop directory. Simply start the utility, click the Raster tab, then type in your desired location for the proxy files. This key must not contain any environment variables, because they will not be expanded.

If you want to share raster proxy files with many users, consider the following:

• The raster proxy folder should be set to the same physical location on disk.
• The raster proxy folder must be writable by all users.
• All users must specify the same named path to the location of read-only rasters—that is, the same drive letter and path designation.

Since you can't remove read-only rasters using ArcCatalog, including rasters on read-only media, it is recommended that you manually remove unnecessary proxy files periodically from this folder to avoid keeping unused files on your hard drive. Although the UAI and AUX files are usually small, OVR and RRD files can grow substantially large, especially when the input raster is highly compressed.