In general, a sitemap is a hierarchical diagram that allows you to visualize the structure of a website. They’re used to define the site’s taxonomy. Taxonomy is a system used to classify things. It’s used to define relationships and similarities amongst content. A website taxonomy makes it easier for users to navigate and to find the content they are looking for. Site maps show us what goes where, and how certain pages are connected.
However, there are several different types of sitemaps.
A visual sitemap looks like a family-tree diagram or flow chart and shows how the web pages relate to each other. Visual sitemaps are also a hierarchical diagram that shows the information architecture of a website. It gives you a visual representation of the site’s organization and how different sections are linked together.
For small websites, I often just create an outline in Word as a visual sitemap. But for medium to large websites, a visual sitemap can help you make sure nothing is left out of the design, nothing is duplicated (that you don't want to duplicate), and can often aid in content creation similarly to an outline.
XML sitemaps help search engines discover the pages on your website by providing them a website’s URLs that create a complete map of all pages on the site. This helps search engines prioritize pages.
The XML sitemap is a file that the user or visitor to the website will see or use. It is specifically designed and built for search engines and to improve the search engine optimization of a website.
An HTML sitemap is a tool for the website user. An HTML sitemap is just a clickable list of pages on a website. These types of sitemaps usually include every page on the website from the main pages to subpages. They help the user find where they are and what the website contains so they can get there.
A website with strong information architecture and navigation systems does not need a sitemap (especially on small to medium-sized sites) since the design of the site should convey to the user where they are and where they want to go.
HTML sitemaps can be helpful in really large websites, especially where the user would like to browse rather than search. I often use the HTML sitemap on Amazon to browse through different genres.
Visual sitemaps are important because they’re one of the first steps in creating a new website (or redesigning an existing one). They're important in organizing and creating content, as well as used as a reference point for wireframes, visual mock-ups, and interactive prototypes.
Because of how they influence the final product, it’s important for clients to provide honest feedback about the sitemap. When reviewing the sitemap, consider whether all pages are represented. Does the organization of the pages make sense? Does the content listed in the sitemap address your users' and business needs? The visual sitemap and a client's feeback regarding it can save a lot of time and trouble down the road by ensuring the project is headed in the right direction from the start.