Match coordinates to regional polygon
On Tue, 10 Mar 2020, Miluji Sb wrote:
Dear all, Re-sending because the message was too big due to the attachment, I am trying to match a large number of coordinates (attached) sub-national regions using GADM shapefile. Coordinates: https://drive.google.com/file/d/1PUsi4d0wP7hB6Aps6UmpXsnIPSD3I1sT/view?usp=sharing Shapefile: https://drive.google.com/drive/folders/1DxyygjQNeg2GIS9doaFM8yM2LvBYZi8E?usp=sharing This is the code I am using; ### library(data.table) library(ncdf4) library(rgdal) library(raster) library(tidyverse)
Apart from rgdal, the remainer are pure distraction. Parsimony is important.
## Read coordinates
coords <- read.csv("coords.csv")
## Read shapefile
world <-readOGR(dsn = "/gadm36_levels_shp", layer = "gadm36_2")
This is the full GADM world map of admin units at level 2:
dim(world)
[1] 45962 13
## Convert to spatial points pts <- coords coordinates(pts) <- ~lon+lat
This is a 0.5 degree world grid
bbox(pts)
min max lon -179.75 179.75 lat -89.75 89.75
SG <- as(as(pts, "SpatialPixelsDataFrame"), "SpatialGridDataFrame") gridparameters(SG)
cellcentre.offset cellsize cells.dim lon -179.75 0.5 720 lat -89.75 0.5 360
bbox(pts)
min max lon -179.75 179.75 lat -89.75 89.75
## Provide the same CRS to the coordinates as the shapefile proj4string(pts) <- proj4string(world) ## Use over function to match coordinates to polygons pts_district <- over(pts, world)$NAME_1 ### However, less than 20% of the coordinates are matched to a polygon. What am I doing wrong? Any help will be greatly appreciated.
plot(pts[!is.na(pts_district$GID_0),], axes=TRUE) looks very much like world land mass to me. Oceans are big, your polygons omit Antarctica, and Plate Carree area (0.5x0.5 degree squares) is misleading. Hope this clarifies, Roger
Regards, Milu [[alternative HTML version deleted]]
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Roger Bivand Department of Economics, Norwegian School of Economics, Helleveien 30, N-5045 Bergen, Norway. voice: +47 55 95 93 55; e-mail: Roger.Bivand at nhh.no https://orcid.org/0000-0003-2392-6140 https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en