Sitemaps are used to plan a web site's purpose, navigation and its overall organization.
They are also used to experiment a site's new structure or re-organize existing structures. You can add, delete or re-arrange the page icons within the sitemap to picture a site's structure.
Visit the Sitemap Shapes page to see what these shapes represent and check out some usage examples.
A list of all the conceptual sitemap and website map shapes available in Creately's library is discussed here.
When it comes to working on a website design project, the usual MO for most is to draw up a sitemap before proceeding towards the design of a wireframe. This would be a logical and the most natural way to proceed, however, there is no reason why you cannot do both in tandem.
Scouring through cyberspace, Google has managed to cough up a gazillion articles on wireframes and mockups but not much on sitemaps. We thought it was time to give you a taste of what the humble but potent sitemap was capable of.