A very useful but often overlooked element of a website is the site map. If
your site is less than 20 or 25 pages you may not need one. However, larger
sites and sites that have problems getting indeed by the search engines can
benefit from a site map.
1) Navigation purposes
A site map literally acts as a map of your site.
2) Conveying your site’s theme
Visitors get the "big picture" of your site at a glance.
3) Site optimization purposes
This allows your site to get crawled by the search engines.
4) Organization and relevance
A site map is an easy way to follow your sites structure when you add on new