Ciao Nikos
Thank you for your comments. I do also have the vegetation types as
independent layers (there are 15 in all). I could of course produce the
result that I need by using Intersect, but this can only be done with
two layers at a time. Although some layers do not overlap, there are
many overlaps and performing this analysis two layers at a time would
be complicated (especially as in a few cases there are more than two
layers overlapping). What I was hoping to find is a way to do intersect
on either (a) many layers together, or (b) of polygons within a single
layer.
Your suggestion to rasterize the 15 layers and work from this is one
possibility (although I haven't thought it through).
There is a grass tool v.patch in the QGIS processing toolbox ('Create a
new vector map layer by combining other vector map layers'). I thought
this would do the trick but it presents an error message near the end
of the process.
Thanks, Martino
On Thu, 2017-09-28 at 15:38 +0200, Nikos Alexandris wrote:
> * Martino <martin.pesca...@inventati.org> [2017-09-28 13:52:25
> +0100]:
>
> Ciao Martino,
>
> > I have a vector layer containing polygons that represent vegetation
> > patches. There are 15 vegetation types (and most have more than one
> > polygon; i.e. the polygons are multipart). Some of the polygons
> > overlap
> > as the areas have more than one classification (e.g. a polygon
> > representing one plant species and a polygon representing another
> > plant
> > species).
>
> Can you derive as many independent layers as the number of vegetation
> types? Manually or better with a small script.
>
>
> > I would like to produce a new layer in which all of the overlapping
> > areas become new polygons. For example, an area of overlap of a
> > patch
> > of Species A and a patch of Species B would become a new polygon
> > representing areas containing both species (and the non-overlapping
> > areas would become separate polygons).
>
> I think having independent layers would be the basis to work on and
> produce the kind of combinatory polygons you are aiming at.
>
>
> > So I start with
> >
> > Polygon with Species A
> > Polygon with Species B
> >
> > and the result would be
> >
> > Polygon with only Species A
> > Polygon with only Species B
> > Polygon with Species A & B
> >
> > I am unable to figure out how to do this!
> >
> > If anybody has any suggestions, I would welcome them.
> >
> > With thanks.
>
>
> If you have Polygon "A" and Polygon "B", then look after
> geoprocessing
> operations. For example, 'Intersection', Union', and the likes should
> give what you are looking for.
>
> Alternatively, if you could work with raster maps, you can think of
> having raster maps for each individual vegetation type, then combine
> the
> maps based on some classification scheme that does include
> combinations
> of vegetation types. Say vegetation type A is going to be assigned a
> pixel value of 1, vegetation type B is going to get a pixel value
> of 2 and then a pixel occupied by A and B is goint to get a pixel
> value
> of 3.
>
> This is an idea to approach the question.
>
> Regards, Nikos
> > _______________________________________________
> > Qgis-user mailing list
> > Qgis-user@lists.osgeo.org
> > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
> > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
>
>
_______________________________________________
Qgis-user mailing list
Qgis-user@lists.osgeo.org
List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
