[Qgis-user] Distance analysis

[Telmo Nunes]

Hello Julio,

There are probably other solutions but here is a possible approach to your
problem. There are also diferent ways to do this in QGIS but here is a
simple solution:

- Convert the ponds layer to a raster layer. You can do this from
Raster->Conversion->Rasterize,
- Create a proximity raster from the created raster layer
(Raster->Analysis->Proximity(Raster distance)
- Install and activate the point sampling tool plugin
- Use the point sampling tool (Plugins->Analyses->Point sampling tool . Use
the point layer with the bird locations as the layer containing the
sampling points and on the lower box select the proximity raster layer and
eventually the fields of your point layer.
The tool will create a point layer and on the table of attributes you will
find one column with the distance to ponds. You can then export that table
of attributes analyse it with your favorite statistical package. That
plugin is realy simple to use and if you decide to consider other variables
you can sample from all layers in just one step.

As I said, there are other ways to do this namelly with Grass or SAGA from
Qgis (Using Sextante plugin), but this approach is quite simple.
Carefull with the CRS definition of your project.

Feel free to PM me if you have trouble with the instructions.

Best regards

Telmo Nunes
Faculdade de Medicina Veterinaria
Universidade de Lisboa
Portugal
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