Hi, It is quite easy to create a web page that shows a cave survey overlay on top of Google / Virtual Earth maps. For an example go to http://www.bdcc.co.uk/mendip.html?Latitude=51.2988&Longitude=-2.7104&Zoom=18 &MapType=Aerial and then select Caves in the overlays drop down (best in Firefox). You will find overlays for Upper Flood (exciting new extensions), Swildons Hole, Manor Farm and Longwood August. I use the Microsoft MapCruncher to generate the tile sets (256x256 pixel PNGs) for Google Maps from a single PDF or .png image. As this is quite a nice way of presenting cave surveys, perhaps a Google tile generator would be a good add on for Therion. The advantage of building the renderer into Therion would be that the overlay could be drawn separately for each Google Zoom level to achieve a good line width and text size. I am well informed in the areas of coordinate systems and map projections and able to program in C++. With some guidance I might be able to help with the coding of such an extension. Regards, Bill Chadwick