Deriving a catchment boundary in GRASS

[Cliff Behrens]

Steve,

It seems to me that you need some criterion for delineating a catchment 
boundary.  For example, I did field work to determine the maximum distance
people seemed to be willing to travel from their village site to clear forest
for gardens or pasture.  Then I used this value to define a circular-shaped
catchment area for each village in my study.  You can use r.digit or s.buffer
to build a map which you can then use as a mask.  Once a data layer is masked,
I have used r.report together with the r.le suite to generate land use/land
cover estimates, composition and other indices used by landscape ecologists.

Cliff Behrens