[GRASS-user] r.watershed: Interpreting Visual Output Map

[Markus Metz]

Rich Shepard wrote:
>   When I read the man page for the visual output map of r.watershed I see
> that it's supposed to help me display results. I assume that it does 
> this by
> coloring the accumulation of surface runoff with sub-basin sizes 
> between 0
> and the threshold value.
Almost right. ...with surface flow accumulation between 0 and the 
threshold value.
>
>
>   How am I to interpret this map? How does 'surface runoff 
> accumulation with
> values modified for easy display' relate to minimum basin size? 
All flow accumulation values larger than the threshold value are set to 
the threshold value.
> What are the
> units of surface runoff accumulation?
Number of cells draining through a given cell. Converted to squared map 
units by multiplying with nsres * ewres, of the flow accumulation map of 
course, and first setting the computational region to match the flow 
accumulation map with g.region -p rast=<my_flow_acc>. -p to check that 
everything is all right.