URL mapping - a feature new to ASP.NET 2.0 - enables page developers to map one set of URLs to another. If a request comes in for one of the URLs in the first set, it is automatically re-mapped on the server-side.
For example, you can configure the application so that the URL ~/Beverages.aspx is mapped to ~/ProductsByCategory.aspx?CategoryID=1&CategoryName=Beverages. With such a mapping in place, when a user enters http://YourSite.com/Beverages.aspx into their browser's Address bar, on the server-side the request will be handled as if they had entered http://YourSite.com/ProductsByCategory.aspx?CategoryID=1&CategoryName=Beverages. The user, however, will continue to see http://YourSite.com/Beverages.aspx in their browser's Address bar; they won't know that the request was re-mapped.
The URL mapping feature in ASP.NET 2.0 is very simple and works by specifying the mapping directly in Web.config. You can read the tutorial at
http://aspnet.4guysfromrolla.com/articles/011007-1.aspx