[GRASS-user] Classify basins as "narrow"

[Markus Neteler]

Forgot to mention:

On Wed, Sep 2, 2020 at 6:28 PM Markus Neteler <neteler at osgeo.org> wrote:
> On Wed, Sep 2, 2020 at 1:27 PM Ken Mankoff <mankoff at gmail.com> wrote:
> >
> > Hi GRASS list,
> >
> > I'd like to detect "narrow" features in GRASS. The attached screenshot shows some basins (thick) and streams (thin) and some regions (hatched). These regions are spurious because the basin is narrow here. I'd like to estimate narrowness with an algorithm.
> >
> > I've looked into r.grow.distance r.distance and v.distance but haven't been able to imagine a solution yet. Can anyone on this list suggest something?
>
> Perhaps the compact measure of
>
> https://grass.osgeo.org/grass78/manuals/v.to.db.html
> --> compact: compactness of an area, calculated as compactness =
> perimeter / (2 * sqrt(PI * area))
>
> could help here?

Related to compactness I found
https://www.azavea.com/blog/2016/07/11/measuring-district-compactness-postgis/

and roughly digitized the shapes presented therein and moved them into
"North Carolina" sample data area with r.region.

The results of v.to.db/compactness are completely different, likely
because it is a different measure from the Polsby-Popper measure used
there.
However, maybe a dataset to play with...

Best
Markus


-- 
Markus Neteler, PhD
https://www.mundialis.de - free data with free software
https://grass.osgeo.org
https://courses.neteler.org/blog
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