Annotating Google Maps

Picture
My local city when I was growing up was Southampton which has some rather impressive historical walls.  I was looking for a map showing the walls and couldn't find any on the web which led me to wondering how hard it would be to add annotations to google maps.  Turns out its dead simple, although the tools for rendering lines and shapes seemed a little rough.  
Click here for a tutorial or explore the map below.

Map of Southampton's Historic Walls


View