HTML Sitemaps are created for the benefit of human visitors to a website. The best way to describe one is as a type of text index, with each entry being a clickable link. Some businesses choose to display this as a 'shortcut' version in their page footer, whilst others have a separate web page with a full Sitemap. An example of a site that does both can be seen here: www.jamieoliver.com.
XML Sitemaps are for the benefit of website crawlers and allow them to easily navigate all levels of a website, including those which are 'deep linked' and could otherwise be overlooked. In addition, an XML Sitemap placed on a new web page can act as a signal to search engines that it exists. Google have confirmed that sites with an XML Sitemap are crawled quicker and in more depth, than those without.
Do I Need a Sitemap?
There is plenty of reading available all over the Internet which demonstrates reasons why you should create either XML or HTML Sitemaps, both or neither! So is there a definitive answer?
There are certainly plenty of rough guidelines and advice from all sides, but perhaps it is best to listen once again to the overwhelming force that is Google, whose advice suggests that both are necessary, with HTML being the slightly more important of the two.
Creating a Sitemap
Having considered the options, the next move is to create a Sitemap. For either type, this is not as daunting as it sounds. If you are already good at coding, it can be done by hand using your favourite text editing program.
If not, there are many free software options available to help you create one automatically in the format of your choice, plus advice pages available from Google Sitemap and tutorials, for additional support.
Aside from the Google implication that Sitemaps can effectively improve your ranking in the SERPs, think also of your visitors. Remember the 'three clicks' rule of website design, allowing visitors to navigate to any part of a site with no more than three clicks? Sitemaps allow this rule to be reinforced and thus improve the overall visitor experience, pretty much a win, win situation.