Google, Yahoo and Live all now support auto-discovery for XML sitemaps. That means you only have to put one line into your robots.txt file to tell the major search engines where to find your XML sitemap (i.e.) in which location have you created

The line looks like:

Sitemap: http://www.example.com/sitemap.xml

Google is allowing people who authenticate their domains (or sub-domains) under one account to include XML sitemaps in one place for all domains or sub-domains. The obvious advantage to Webmasters is that they can create one primary XML sitemap repository and keep that up-to-date. so the crawler can easily crawl and index your page.