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The idea to transfer vector data instead of images and render it on the client side is not new. There are already a lot of tools/projects doing that. See for example this plugin of leaflet, polymap, and also the cartagen project. OpenLayer developer are trying to introduce it in the (long-awaited) version 3.0. Each of these initiatives use their own vector ...


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Idea how to make an outside clip: Make an Extent layer of your raster layer (Polygon from Layer-Extent in Vector Menu) Do a symetrical difference (also in Vector Menu) with your polygons Use the resulting layer in gdal to clip your raster layer (clipper in Raster menu) Then you could just do your zonal statistics or whatever you want to do with the cell ...


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There's two ways you could do this. One is to wrap your field that contains some nulls by the 'coalesce' function: Coalesce("tree_field_name", '0 trees') This would use the value in tree_field_name if it's non null, otherwise it will use the string '0 trees' (pay attention to the use of " and '). The alternative is to use a "case when" function: Case ...


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Euclidean Distance and Zonal Statistics (As Table) will tell you the average distance to the closest point for each polygon. It's worth considering that Euclidean distance is not walking distance. Walking routes are restricted: a person can't (reasonably) walk over a building, an interstate highway, a river/stream, etc. A more accurate method would be to ...


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for the average walking distance to the closest point, you can indeed use the Euclidian distance to create a raster of the distance to the closest point. Then you can compute the average distance using zonal statistics (or zonal statistics as a table if you prefer a vector output)


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Well, you can do that using ogr2ogr, after exporting vectors from GRASS to shp: ogr2ogr -sql "SELECT * FROM file_in WHERE 'category' == 2 AND OGR_GEOM_AREA > 10000" file_out.shp file_in.shp file_in.shp is your data exported from GRASS file_out.shp is your filtered results. Then you can run: ogr2ogr -sql "SELECT count(OGR_GEOM_AREA) FROM file_out" ...


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I'd add my answer as a comment, but since I can't comment (no reputation enough), I'll add as an answer. It seems that you are trying to add centroid connectors to feed into a traffic assignment algorithm. Right? I should say that doing it automatically is not considered best practice in this industry, but it you are going to do it, I'd like to suggest you ...



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