There are two types of maps, direct and indirect. Indirect maps are the most common, here the map identifies the name of each directory and the associated system and directory to mount. Direct maps put more burden on the system in that they can result in a furry of mount activity. This is because indirect maps do not mount file systems until you enter the directory. Direct maps mount the file system when you access it via a directory listing.
Side affects of using the automounter.
If you include many directories handled by the automounter you could experience significant delay when your .cshrc file is executed. This is caused by the shell going out and reading each directory to get the contents for the executable hash table. One solution, is to create wrapper scripts in another directory not handled by the automounter that modify your path and invoke the utility. Performing a ls at the mount point will not list the files found in each directory, instead just the symbolic link names will be listed. This can confuse users and applications.