Typically you can display information as a network diagram, with items of information (documents, web pages, scholarly papers) represented by nodes in the diagram (usually circles or squares) and the relationships between them by connecting lines. Sometimes the lines are labeled with text captions and have arrows indicating the direction of the arrows (in which case it is technically known as a directed graph).
Some forms of diagrams have more restrictions, for example the diagram showing the hierarchy of sections and chapters in a book or the site map showing web pages on a web site. Part of the process of composing written work may be seen as taking a spaghetti diagram of seemingly randomly connected information and turning it into a neat hierarchy suitable for publication.
In teaching web site design I suggest to the students that they can think of trimming the directed graph of interconnected web pages into a site map. This is not to say that all the other links which don't fit in the neat tree structure are deleted, just that they are considered less important by the designer. These extra links will become hypertext links within the text of the document, whereas the main links are usually in menus on separate web pages or sections. In a printed document the main links are represented by the table of contents and by the physical ordering of the content; other links by cross references, indices and the like.
Web search tools work in part by making automated decisions as to how to arrange blocks of information. They partly use the hypertext links inserted by the author, but also use the text itself to make connections the author could not see.
While there are document creation tools for web designers and writers which allow direct manipulation of diagrams, my impression is that most authors have difficulty conceptualizing information this way. They see information as strings of words and are more comfortable cutting and pasting text, than moving icons and links. But this might be a bias introduced by "word processors" being the tool they are first introduced to.
KartOO is a search engine which displays the results as a diagram. Collections of documents at each web site are shown as icons (with size representing importance). Web sites are linked by lines labeled with words indicating what they have in common. In the background are shaded regions showing general concepts. When you place the pointer over a document, the links to other related documents are highlighted. This can be useful for seeing relationships between information, people and organizations. But I don't find it much use for day to day web searching.
As an example, searching with Kartoo for "Tom Worthington" shows the largest collection of documents at my web site tomw.net.au and a smaller collection at my professional body acs.org.au these are related by the words: technology, Industry and committee. Placing the pointer over the largest document, which is my biography, shows links from it.
Flickr and Del.icio.us provide a Folksonomy, with items of information manually tagged by any contributor. A diagram typically displays the relative impotence of tags by the size of the text. This might provide some insights into to content, but I have not found it that useful.
A folksonomy is an Internet-based information retrieval methodology consisting of collaboratively generated, open-ended labels that categorize content such as Web pages, online photographs, and Web links. A folksonomy is most notably contrasted from a taxonomy in that the authors of the labeling system are often the main users (and sometimes originators) of the content to which the labels are applied. The labels are commonly known as tags and the labeling process is called tagging.
The process of folksonomic tagging is intended to make a body of information increasingly easier to search, discover, and navigate over time. A well-developed folksonomy is ideally accessible as a shared vocabulary that is both originated by, and familiar to its primary users. Two widely cited examples of websites using folksonomic tagging are Flickr and Del.icio.us, although it has been suggested that Flickr is not a good example of folksonomy.
From: Folksonomy, Wikipedia, 2006
The website del.icio.us (pronounced as "delicious") is a social bookmarking web service for storing, sharing, and discovering web bookmarks. The site came online in late 2003 and was founded by Joshua Schachter, co-maintainer of Memepool. It is now part of Yahoo!.
A non-hierarchical keyword categorization system is used on del.icio.us where users can tag each of their bookmarks with a number of freely chosen keywords (cf. folksonomy). A combined view of everyone's bookmarks with a given tag is available; for instance, the URL "http://del.icio.us/tag/wiki" displays all of the most recent links tagged "wiki". Its collective nature makes it possible to view bookmarks added by similar-minded users.
From Del.icio.us, Wikipedia, 2006