The Sitemap 0.90 protocol is an open standard supported by the main search engines including Google, Yahoo!, and Microsoft Bing.
Similar to RSS feeds it uses XML to represent the contents of your website in a structured format.
It contains 4 elements for each page in your website :
An example of a sitemap file can be seen below :
<?xml encoding="UTF-8" version="1.0" ?>
<?xml version="1.0" encoding="UTF-8"?>
The Sitemap protocol can be extended to include other elements. Google utilises this fact to include media files such as images within the sitemap.
G-Mapper will index images in your pages and include them in your sitemap.
You can find out more about th sitemap protocol at www.sitemaps.org.
However all you need to know is that google supports the format and with a few clicks you can create and submit yours.