ArcGIS stores its persistent information in Windows files. The Windows file system is organized into drives (once upon a time these were actual physical disk drives), which contain files and/or folders. (A folder is just a special kind of file in which Windows stashes information about other files or folders.) Together, drives, folders, and files implement a simple hierarchical information management system, which lets you group bags of information (files) into nested categories (folders).
The combination of a drive name, one or more folder names, and a file name is called a pathname. Windows pathnames are written as follows:
A pathname that doesn't begin with a drive letter is called a relative pathname. A relative pathname is assumed to have the pathname of the current folder prepended to it.
\is assumed to have just the current drive prepended to it
\ESM2631\is the same folder as
The special folder name
.. (two periods) is often
used in relative pathnames to refer to the parent folder
of the current folder.
H:\arf.txtboth refer to the same file.
Windows also recognizes a network name (of the form
that is sometimes used instead of a drive letter.
H:\ whenever you log into a Bren computer.
This is handy because it means we can refer to your personal
home folder as
H:\, regardless of who you are.
Pathnames beginning with a network name are called UNC pathnames. (UNC means Universal Naming Convention, which means that only Microsoft uses it...)
IMPORTANT: While most (but not all!) of Windows supports UNC pathnames, much of ArcGIS does not. They can trigger all kinds of misleadingly-reported errors. Don't use them! Always refer to files with either relative pathnames, or pathnames beginning with a drive letter.
Any time you're working on Windows, there's a notion in effect called the current folder (AKA the working folder). For a Windows application, the current folder is usually the folder containing the document that it was started up with.
When working with ArcGIS, it's essential that you follow these rules when creating new files or folders:
Breaking any of these rules will result in a file and/or folder name that may work just fine in Windows, but may be inaccessible to ArcGIS. When this happens, the ArcGIS error message won't give you the least clue what's going on...
If you'd like even more detail on how filenames work (or don't work), see: