It doesn't matter if those locations are Web pages or street addresses, since the goal of 'getting the user where she wants to go' is still tantamount. The explosion in online communications is calling into question all the indexing rules developed around books over the last 200 years. If we can't find it, it might as well not exist. I would also argue that any navigationally oriented web page is an index. The value of information is in how it can be found and used, and the index is the key.
Online communication opens up whole new avenues for more intuitive indexing.
Every time you do any of these things, you are calling upon an online index. Online indexes need to be written with the goal of recreating that lost context. Links can be organized chronologically, geographically, metaphorically, by task, by importance, or by some other custom scheme. While savvy Web developers and designers may understand and apply these concepts intuitively, Seth says that it's hard for most people, particularly traditional indexers, to think of a clickable map as an index, particularly because the Web is not yet 10 years old. An image map serves the same purpose as an index, only without words.