In addition, each of these visualizations can be customized via the drop-down menus that appear in the top left of the Visualization dialog. Here's what those menus do:
Type. Determines which kind of visualization will be displayed (see links below for details on each visualization type).
Content. There are two content menus: the first selects the initial set of content to be visualized (i.e. all pages, paths, media, etc.), and the second allows you to add a set of items which are related to the first set (i.e. all children, parents, etc. of those initial items).
Sort. The two sort menus allow to specify the type of sort to be applied to the results (i.e. alphabetical, by creation date, etc.), and the ordering of that sort (ascending or descending). Note that sorting only has a visible effect in the Grid and List visualization types.