Polygon Data into Grid Structure
On Mon, 2 May 2022, lucfrank at mail.uni-mannheim.de wrote:
Hello everyone, I have the Aqueduct 3.0 Data from the WRI Institut which is in Multipolygon format.
This is not clear, neither aqueduct nor WRI mean anything to me and possibly most others.
To perform a regression analysis with different datasets I want to transform these polygons into a grid. Basically, I want to overlay a grid over the map and assign each cell the value of the underlying polygon. In a second step, I want to count how many points (different dataset) are inside each cell.
So a standard intersection between a raster grid and polygons - but you are modifying the support of the data quite brutally. If you need to integrate data with varying support, do not treat the estimated values for the new entities as fixed, they are estimates with error distributions. Why not simply count the points within each polygon?
I have tried with the sp commands GridTopology, and SpatialPoints. I can produce the grid but fail to crop with my map. Also, it is not clear to me how I can assign the underlying value of the polygon. This is the code I have tried so far: (I have copied this from doing a Course on DataCamp which I can't completely copy exactly because my data is different)
Not a robust idea; build up your analysis from the support of your own data based on robust sources.
# -25,-49 my lower left corner (these are coordinates) grid <- GridTopology(c(-25,-49),c(1, 1), c(72, 48))
This looks rather odd, seeming to use geographical coordinates, so the areas in the grid cells vary with latitude (as would the counts).
gridpoints <- SpatialPoints(grid, proj4string = CRS(projection(aqua))) plot(gridpoints) cropped_gridpoints <- crop(gridpoints, aqua) plot(cropped_gridpoints)
crop is from terra (in older workflows raster), not sp. Perhaps using terra for the whole exercise is advisable? Your workflow template doesn't seem to be current, or even adequate, I'm afraid. Roger
spgrid <- SpatialPixels(cropped_gridpoints) plot(spgrid) I hope someone has an idea to help me solve this. Thanks to everyone who has any insights into this Luca Frank
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