A site map lets the search engine know about the existence of pages it might not have discovered through spidering through your site normally.
Ideally, you should create a normal HTML site map for your users and an XML site map for the search bots. If at all possible, link both.
Distance makes a difference – further from the home page the bigger the click distance the less important it must be.
Hierarchy reflects importance and relevance.
From a talk given at the British Library on SEO by Lucidica on March 4th 2010. An IT company based in London.
Links
Lucidica website
lucidica.com
