The site map is a mechanism for mapping an acs_object to a URL. The most common object mapped in this manner is an ACS package instance.

Most packages can be mounted any number of times, at any point in the site map. In particular the acs-subsite can be mounted to provide a new site community, with its own set of members, content packages (forums, blogs, etc), and look-and-feel. This is similar to the way in which .LRN provides classes, clubs and communities, each of which has its own members (professors etc), and each type its own color scheme.

When the OpenACS core is installed, an instance of the acs-subsite package is mounted at the root node ("/") of the site map.

A package instance can find out where it's mounted by the use of utilities in the site-nodes utility library (found in the acs-tcl package). A package instance normally keeps track of the content it has created by storing its object_id in the "package_id" column in the base acs_objects table.