Sitemaps instructs the search engines a structural way of accessing a website’s URL.Search engines periodically crawls your website to index the web pages,sitemap.xml file in the web server provides the search engine the information about the web pages and which pages should and should not be accessed.Successful SEO starts with the creation of correct sitemaps. [more]
There are several tools to create sitemaps online like XML sitemaps which creates sitemap.xml file that is used by search engines to crawl the website.
Visual way of telling the contents of the website.It is easily understandable by the visitors and its easy to create.Visual sitemaps are useful when you are planning for new website and want to see the structure of the pages.
using write maps you can create visual sitemaps easily,you can also export this sitemap in XML format.
As far as designers are concerned visual sitemaps are useful when starting a fresh design and while creating tutorials because it visually explains the structure of the site.