The OneGeology website gives its mission as:
Make web-accessible the best available geological map data worldwide at a scale of about 1: 1 million, as a geological survey contribution to the International Year of Planet Earth.
While the official launch of the site is scheduled to coincide with the International Geological Conference in Oslo, August 6-14, the mapping portal site is already partially functional, although a few bugs and quirks still exist. It currently works with Internet Explorer 6/7, and Firefox 2, but not Firefox 3 (hope this changes soon). And while the goal is to have data for the whole world at a 1:1,000,000 scale, data for significant areas of the world are currently not available at that scale; for example, the US data is at the 1:5M scale. A partial list of the WMS data available and its scale is on this page.
When you start up the portal, NASA’s Blue Marble imagery will be the default display. To add a layer of geological data registered with the site, click on the Add Layer button and select the desired geological data from the list that pops up:
You can also add a layer from another WMS site by clicking on the “External layers” tab and entering the web address for the WMS; this can be any kind of data, not just geological. By clicking on the “Active layer properties” arrow, you can bring up a dropdown that lets you set the draw order of the layers, their visibility, opacity, and the option to delete them entirely; clicking on the arrow in the layer info section brings up another dropdown with more options:
The left-hand corner holds standard commands for zooming, panning, refreshing, and an overview map that shows you the location you’re currently looking at:
If you click on the “i” icon, then click on the map, a pop-up window will give you info on what the rock type is at that location (although this is still a little buggy):
You can also save the current state of the WMS screen, with the layers and zoom level, as a WMC file on your computer that can be re-loaded at a later time at this site, or create a KML file that will load the data layers into Google Earth:
The site’s still in its infancy, and both data and functionality are still works in progress, but this is already nirvana for geology nuts like me.