SF Neighborhoods using an undocumented GPolygon feature in the current Google Maps API v2.49. I've extracted and cleaned up the code a bit so that you can use polygons yourself. Just take a look at poly.js and add this after you add the API javascript. Then you can use GPolygon with only a few caveats:

• You have to use v2.49 for now b/c some functions are referenced by their obfuscated name in this particular version of the API
• I've only tested this on Firefox 1.5 (using SVG) and IE (using VML).
• The code to clean up event handlers when an overlay is removed is kinda broken, so you will probably get memory leaks
• Event handlers like onclick and onmouseover don't work.

I think of this code as a preview of what's to come. Try it out before it's actually released, I guess.

To create a new polygon, call new GPolygon(polylines, fill?, color?, opacity?, outline?). polylines is an array of GPolylines, fill is a boolean indicating whether you want the polygon filled or not, color is the color of the polygon's interior (the outline color is determined by the polylines), opacity determines the fill's opacity, and outline is a boolean determining whether the outline polylines are drawn or not.

Enjoy! (Chris Smoak - 3 May 2006)