On 06/07/17 16:16, Sergio Ibarra wrote: > Hello everyone > > In my work, I use to intersect polygon grids with lines or points. I use > the package "sf" with the function 'st_intersection". However, every time I > run st_intersection I got the following Warning Message: > > Warning message:attribute variables are assumed to be spatially > constant throughout all geometries > > > What does this warning mean?
Attribute values are assigned to sub-geometries; if these are spatially constant, as for instance for land use, then this is fine. If they are aggregates, such as population count, then this is not fine, wrong even. By default, they are set to NA. e.g. demo(nc) st_agr(nc) = "constant" takes away the warning, as it sets all attribute values (in this case wrongly) to "constant", as of their agr value (agr standing for "attribute geometry relationship"). More here: https://cran.r-project.org/web/packages/sf/vignettes/sf1.html#how-attributes-relate-to-geometries > > Thanks > -- Edzer Pebesma Institute for Geoinformatics (ifgi), University of Münster Heisenbergstraße 2, 48149 Münster, Germany; +49 251 83 33081 Journal of Statistical Software: http://www.jstatsoft.org/ Computers & Geosciences: http://elsevier.com/locate/cageo/
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