[R-sig-Geo] Country names from coordinates

[Bacou, Melanie]

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
>
> 	[[alternative HTML version deleted]]
>
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at r-project.org
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo