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10027: Layer's data source is referenced via a UNC path

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Accessing data using UNC paths uses network file access instead of direct disk access, which will affect display performance.


Check the drawing performance for your layer or basemap layer in ArcMap. If you are publishing, check the drawing performance for your service in the Preview window.

Learn more about working with basemap layers or previewing your service

  • If you see the need to make changes, evaluate the drawing performance of map layers that use UNC paths. If possible, make a local copy of the data sources on your computer's disk drives and use absolute paths. This may significantly improve drawing performance.

More information

A path specifies a unique location in a file system by describing the hierarchy of directory folders and files on a computer network. An absolute, or full, path begins with a drive letter followed by a colon. For example:


UNC paths use a syntax for specifying folders and files on a network of computers. UNC stands for Universal (or Uniform, or Unified) Naming Convention. The syntax is as follows:

\\<computer name>\<shared directory>\

followed by any number of directories and terminated with a directory or file name. For example:



In ArcGIS, you can use an absolute or UNC path anywhere a path is requested. Using a UNC path is particularly advantageous for shared data on a local area network (LAN). Data can be stored on one computer and everyone with access to the computer can access the data via its path.

There may be a performance disadvantage when using UNC paths because network file access is typically slower than direct disk access on your local computer (using absolute paths), which can affect map drawing performance.

Absolute paths can also be specified using a relative path, in other words, a location that is relative to a current directory. Relative paths do not have an impact on map drawing performance.

Learn more about referencing data in ArcMap using paths and making your data accessible to ArcGIS Server