Linden Lab Official:Map API Introduction
What is the Map API?
Extend the reach of your Web site into Second Life using the Second Life Map API, which enables you to embed interactive Second Life maps directly into your web pages. These maps look and act much like Google Maps, except that, instead of the Earth, they display the topography of the Second Life virtual world. See http://maps.secondlife.com/ for an example.
When you use the Map API to embed Second Life maps on your site, your visitors can:
For more information, see the Map API documentation.
What is DirectSLurl?
DirectSLurl is a web-to-inworld URL that teleports users to a specified Second Life location when they click on a special web-based URL, known as a SLurl. If the user has already installed the Second Life Viewer, then the Viewer starts and they are automatically given a dialog box to teleport to the location specified by the SLurl. If the user doesn't have an account, they are sent to the Second Life registration page; when they complete registration, download, install, and run the client, they automatically start at the location specified by the SLurl. DirectSLurl is an easy way to bring people to your location in Second Life without the programming requirements of the Registration API. You don't even need to use the Map API to take advantage of DirectSLurl, though you can use both for a more customized user experience. For more information, see Using Second Life URLs (SLurls) on the Second Life Wiki.