[GRASS-user] r.flow: units for flow accumulation

Rich Shepard rshepard at appl-ecosys.com
Fri Oct 19 08:37:12 PDT 2018

On Fri, 19 Oct 2018, Micha Silver wrote:

> If my understanding is correct, the r.flow module output raster
> "flowaccumulation" gives (as in manual that you quoted) the *number* of
> flow lines flowing into each cell. This is not upstream contributing area
> in the usual sense. Rather it describes stream density. If you check the
> values in cells that are downstream right in the streams, you'll see that
> they have a low value (i.e. small number of upstream flow lines that end
> in that cell). 


   Thanks for clarifying.  I thought that r.flow's 'flowlines' output did
the above. Reading the manual page again suggests, to me, there are very
subtle differences among flow lines, flow paths, and flow accumulation.
Perhaps this is not what I need to present.

> If you want the actual upstream contributing area (flow accumulation in
> the usual sense) then go back to the r.watershed module and use the
> "accumulation" output option. Then, your non-technical audience will
> easily understand the legend referring to "upstream contributing area".

   Gotcha'. I'll do this instead of using r.flow.

Best regards,


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