Country names from coordinates
Here is an approach using raster::extract(). I assume your point
locations are unprojected.
library(raster)
library(tmap)
data(World)
proj4string(World)
# [1] "+proj=eck4 +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84
+units=m +no_defs +towgs84=0,0,0"
pts <- SpatialPointsDataFrame(temp [, c(1,2)], temp,
proj4string=CRS("+init=epsg:4326"))
# Reproject World
World <- spTransform(World, CRS("+init=epsg:4326"))
# Extract and append World attributes at pts point locations
pts <- extract(World, pts, sp=TRUE)
--Mel.
On 7/25/2016 9:01 AM, Miluji Sb wrote:
I have the following data at 0.5 degree by 0.5 degree.
temp <- dput(head(ptsDF,10))
structure(list(longitude = c(-68.25, -67.75, -67.25, -68.25,
-67.75, -67.25, -71.25, -70.75, -69.25, -68.75), latitude = c(-54.75,
-54.75, -54.75, -54.25, -54.25, -54.25, -53.75, -53.75, -53.75,
-53.75), GDP = c(1.683046, 0.3212307, 0.0486207, 0.1223268, 0.0171909,
0.0062104, 0.22379, 0.1406729, 0.0030038, 0.0057422)), .Names =
c("longitude",
"latitude", "GDP"), row.names = c(4L, 17L, 30L, 43L, 56L, 69L,
82L, 95L, 108L, 121L), class = "data.frame")
I would like add the corresponding country names to each of the
coordinates. This is what I have done:
library(data.table)
library(rgdal)
library(reshape2)
library(dplyr)
library(tidyr)
library(lubridate)
library(maps)
library(countrycode)
library(ggplot2)
library(raster)
coord_cells <-temp [,c(1,2)]
pts_cells <-
SpatialPoints(coord_cells,proj4string=CRS(proj4string(worldmap)))
indices_cells <- over(pts_cells, worldmap,na.rm=TRUE)
foo_cells<-indices_cells[,c(3,5)] # Keep ISO3 and country names only
new_data <- cbind(foo_cells, temp)
However, I get a large number of NAs for coordinates which should have
corresponding countries. What am I doing wrong? Any suggestions? Thank you.
Sincerely,
Milu
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