>Colour by Altitude

Is it possible to colour by altitude along the wall edges only ?

I do not want the scrap filled with colour, just a colour edging along the walls, either inside or outside and preferably able to define the colour width. Perhaps add a feature to the colour fill function to allow the user to specify complete fill or edge width plus inside/outside ?

Have a look at the metapost for the built in line definitions.  It might be possible (once you have deciphered how metapost works) for you to replace the standard wall definition with a custom one of your own.

There are examples that show how to create an offset line in the existing code, (line wall subtype pit, and subtype over or underlying) so this could be modified to create a narrow boundary to fill with the map-fg colour (altitude in this case).

See http://therion.speleo.sk/wiki/doku.php/metapost to get started.

Bruce