Pathnames explained: Absolute, relative, UNC, and URL
Release 9.2 Last modified November 9, 2007	Print all topics in : "Sharing tools and toolboxes"

You deal with pathnames every day to browse to your data and toolboxes. You probably don't give them much thought, nor do you need to, until it comes time to share your data and tools. This section delves into detail about pathnames, defining the different types and how ArcGIS manages them. Subsequent topics on sharing tools assume that you've reviewed the material presented here.

Path and pathname

A path is a slash-separated list of directory names followed by either a directory name or a file name. A directory is the same as a system folder.

E:\Data\MyStuff            (path terminating in a directory name)
E:\Data\MyStuff\roads.shp  (path terminating in a file name)

NOTE: In everyday usage, path and pathname are synonymous. Pathname is sometimes spelled path name.

Forward versus backward slashes

The Windows convention is to use a backward slash (\) as the separator in a path. UNIX systems use a forward-slash (/). Throughout Windows and ArcGIS, it doesn't matter whether you use a forward or backward slash in your path. When using the UNIX operating system, you must use a forward slash. ArcGIS will always translate forward and backward slashes to the appropriate operating system convention.

System versus catalog path

In ArcGIS, you'll sometimes come across the term catalog path or ArcCatalog path. A catalog path is a pathname that only ArcGIS recognizes. For example:

D:\Data\Final\Infrastructure.mdb\EastValley\powerlines

refers to the powerlines feature class found in the EastValley feature dataset in the personal geodatabase Infrastructure. This is not a valid system path as far as the Windows operating system is concerned, since Infrastructure.mdb is a file, not a folder, and Windows doesn't know about feature datasets or feature classes. Of course, everything in ArcGIS knows how to deal with catalog paths.

Absolute and relative pathnames

Absolute, or full, path

An absolute, or full, path begins with a drive letter followed by a colon, such as D:

Relative path

A relative path refers to a location that is relative to a current directory. Relative paths make use of two special symbols, a dot (.) and a double-dot (..), which translate into the current directory and the parent directory. Double-dots are used for moving up in the hierarchy. A single dot represents the current directory itself.

In the example directory structure below, assume you used Windows Explorer to navigate to D:\Data\Shapefiles\Soils. After navigating to this directory, a relative pathname will use D:\Data\Shapefiles\Soils as the current directory (until you navigate to a new directory, at which point the new directory becomes the current directory). The current directory is sometimes referred to as the root directory.



If you wanted to navigate to the Landuse directory from the current directory (Soils), you could type in the following in the Windows Explorer Address edit box:

..\Landuse

and Windows Explorer would navigate to D:\Data\Shapefiles\Landuse. A few more examples using D:\Data\Shapefiles\Landuse as the current directory are

..               (D:\Data\Shapefiles)
..\..            (D:\Data)
..\..\Final      (D:\Data\Final)
.                (D:\Data\Shapefiles\Landuse - the current directory)
.\..\Soils       (D:\Data\Final\Soils)
..\..\.\Final\..\Shapefiles\.\Landuse  (D:\Data\Shapefiles\Landuse)

NOTE: A relative path cannot span disk drives. For example, if your current directory is D:, you cannot use relative paths to navigate to any directory on E:

Absolute and relative pathnames in ArcMap

You cannot enter relative pathnames using the dot/double-dot notation described above in any ArcGIS desktop application. However, when you create an ArcMap (or ArcScene or ArcGlobe) document, you can specify that pathnames will be stored as relative pathnames. (Absolute pathnames are the default.) To set this option, look under the File menu, click Document Properties, then click the Data Source Options button found on the lower right. This will open the Data Source Options dialog box, and you can specify whether to store absolute or relative paths.



When you save the document with relative pathnames, the application converts all pathnames into relative pathnames (using the dot/double-dot notation) in relation to the location where you stored the document. For example, if your document is stored in

D:\Maps\Posters\Newmap.mxd

and the data in one of your layers is

D:\Data\Final\Infrastructure.gdb\Streets

what gets stored in Newmap.mxd is

..\..\Data\Final\Infrastructure.gdb\Streets

When you open Newmap.mxd again, ArcMap converts the stored relative pathname from the dot/double-dot notation back into the absolute path representation, which is displayed as the data source for a layer. Note, however, that if you move Newmap.mxd to another directory, the data will not be found.

Learn more about referencing data in a map

Absolute and relative paths in geoprocessing tools

Just like data in ArcMap, you can specify that pathnames in your tools are to be stored as relative paths. The current directory used for relative paths is the directory where the tool's toolbox resides.
The relative pathname option converts paths to

• Data in a model
  
• Script files
  
• Graphics in a model
  
• Compiled help files (.chm).
  

To store as relative paths, right-click the tool and click the General tab. At the bottom of the dialog box, check Store relative path names (instead of absolute paths), as shown below.



When you add a script tool, this option will also appear on the first panel of the Add Script wizard. Setting this option on the Add Script wizard is the same as setting it on the tool's property dialog box, so you can always reset this option when the Add Script wizard is completed.

Why use relative versus absolute pathnames?

Using absolute pathnames:

• You can move the document or toolbox anywhere on your computer and the data will be found when you reopen the document or tool.
  
• On most personal computers, the location of data is usually constant. That is, you typically don't move your data around much on your personal computer. In such cases, absolute pathnames are preferred.
  
• You can reference data on other disk drives.
  

Using relative pathnames:

• When moving a document or toolbox, the referenced data has to move as well.
  
• When delivering documents, toolboxes, and data to another user, relative pathnames should be used. Otherwise, the recipient's computer must have the same directory structure as yours.
  
• You cannot reference data on other disk drives.
  

For example, consider the directory structure below. In this example, D:\Tools\Toolboxes\Toolbox1 contains a script tool that uses D:\Tools\Scripts\MyScript.py.



Using absolute paths, if you moved the toolbox from

    D:\Tools\Toolboxes\Toolbox1

to a different disk, such as

    E:\Final\Toolbox1

ArcGIS will find D:\Tools\Scripts\MyScript.py and everything will work fine. If, however, you use relative paths, ArcGIS will not find the script and the tool will not work. The tool dialog will open but when you execute you'll get the error message "Script associated with this tool does not exist". You will have to open the tool's Properties and enter the correct pathname to the script. At the same time, you should probably uncheck the Store relative pathname option.
On the other hand, if you use relative pathnames, you can simply copy the folder D:\Tools anywhere on anyone's computer and everything will work. This won't work if you use absolute paths, because the recipient could copy the folder to F:\NewTools and the pathname D:\Tools\Scripts\MyScript.py won't exist on their computer.

Summary

• Relative paths cannot span disk drives.
  
• Absolute pathnames work best when data isn't moved, which is typical for disks on a personal computer.
  
• Relative pathnames work best when you're delivering documents and data to another user.
  
• Relative pathnames use dot/double-dot (. and ..) notation. You can enter relative pathnames with this notation in Windows Explorer or at the Windows command prompt.
  
• ArcGIS doesn't allow you to enter relative pathnames using dot/double-dot notation. Rather, relative pathnames are stored in the document or toolbox (once you check the Store relative pathnames option).
  
• Relative pathnames are relative to a current directory, which is the location of the saved document or toolbox.
  

UNC pathnames

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

\\<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

The computer name is always preceded by a double backward-slash (\\).

In UNC, the computer name is also known as the host name.

A few rules for UNC pathnames are

• UNC paths cannot contain a drive letter (such as D:).
  
• You cannot navigate to directories above the shared directory.
  
• The Store relative pathnames option for documents and tools has no affect on UNC pathnames.
  

In ArcGIS, you can use a UNC pathname anywhere a pathname is requested. This is particularly advantageous for shared data on a local area network (LAN) or wide area network (WAN). Data can be stored on one computer and everyone with access to the computer can use the data.
There are two issues with sending documents or tools that contain UNC paths.

• The recipient doesn't have access to your computer, either because of security settings on the shared directory, or because they don't have access to your LAN.
  
• The computer or its shared folder is removed from the network.
  

In Windows, you can share a folder so that other users on your local area network can access it. In ArcCatalog or Windows Explorer, right-click a folder, click Sharing and Security, then follow the instructions on the dialog box that opens.

URLs

URL stands for Uniform Resource Locator, and uniquely specifies the address of any document on the internet. The components of a URL are:

• The protocol used to access the resource, such as http (HyperText Transfer Protocol) or ftp (File Transfer Protocol)
  
• The host (server) to communicate with
  
• The path to the file on the host
  

For example:

http://www.esri.com/products.html

Windows Internet Explorer allows you to type "www.esri.com" in the Internet Explorer address bar, and it will add http://. It's more correct, however, to specify the protocol, such as http. Other protocols include https (Secure HyperText Transfer Protocol), ftp (File Transfer Protocol), mailto (E-mail address), and news (Usenet newsgroups), among others.

In ArcGIS, you can only use URLs where permitted. In general, the user interface will tell you whether a URL is permitted or needed. In geoprocessing, URLs can be used in the Documentation Editor when creating links, or in labels within ModelBuilder. When using URLs in ArcGIS, it's recommended that you include the protocol, as in

http://www.esri.com

rather than

www.esri.com

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