You may (or may not) like to see the result of the discourse on Mercator. This image has been adjusted for Latitude at 57°N (but is NOT a Mercator projection), and should be viewed in the maximum colours your computer can handle (the original has 16 Million colours). The whole image is colour-coded. With the deliverable software, as you move the mouse over the image, it tell you the height or depth under the cursor. As matter of interest, processing the data to create images for the whole world takes around 36 hours non-stop on a G4/500. http://www.btinternet.com/~philyates/downloads/uk.jpg (596K) Phil.