Originally Posted by jamesj
there are two sitemap
1) html sitemap
2) xml sitemap
In which html sitemap will be helpful to your website visitors to find a list of page and select the page they looking for where as xml sitemap will help search engine crawlers to find the pages which are not visible for them in simple crawling or links hidden by iframe, ajax, flash etc.
One might ask why two sitemaps are necessary.
The answer is obvious - one is for humans, the other is for spiders (for now mainly Googlebot but it is reasonable to expect that other crawlers will join the club shortly).
In that relation it is necessary to clarify that having two sitemaps is not regarded as duplicate content. In 'Introduction to Sitemaps', Google explicitly states that using a sitemap will never lead to penalty for your site.