[mapserver-users] An intellectual exercise

[Steven Hayes]

Hi All,

I am rolling out a 2m contour layer on an existing application focused on
environmental education. The contours are coloured based on height giving a
quasi 3d effect:

http://www.streamwatch.org.au/gisdemo

It would be a truly fantastic educational resource if a user could click
somewhere on the map and have an arrow drawn showing which way runoff will
flow based on some kind of algorithm that calculates the nearest two contour
lines and works out which is the highest and perhaps their angle with
respect to each other. I am using mapscript and can already return shape
indexes etc (thanks to the help of several on this list) but I am not sure
how to approach this kind of query - if indeed it can be done.

Any ideas anyone?

Regards

Steven Hayes