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

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

Solution

• Check the drawing performance of your basemap layer in ArcMap or your map service in the Preview window. See Working with basemap layers or Publishing map services for more information.
• 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, such as D, followed by a colon. For example:

D:\Data\Final\EastValley\powerlines

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:

\\pondermatic\public\studyarea.gdb
\\omnipotent\shared_stuff\wednesday\tools

In ArcGIS, you can use an absolute or UNC path anywhere a path is requested. This 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.

See Referencing data in the map for information about using paths in ArcMap.