I have downloaded and installed libraries terra and geodata in R.
I am now trying to give a list of coordinate pairs (lon,lat) and find out which country (or US state) it is in. the right start is
library(geodata)
usa <- gadm(country="USA", level=1, path=tempdir())
wld <- world(path=tempdir())
I know from a plot(usa) and plot(w) that I now have the map coordinates down to the state level for the US and the full world map, but I don't know how to inquire about (lon,lat) points. Point ers to the right function would be appreciated.
Added: I obviously was not clear enough. The question and answer (thx, robert) were indeed:
> mypoints <- rbind(c(lon=-100,lat=34),
c(-118,34),c(-90,40),
c(-80,40),c(-73.961,40.786))
> terra::extract(usa,mypoints)
id.y GID_1 GID_0 COUNTRY NAME_1 VARNAME_1 NL_NAME_1 TYPE_1 ENGTYPE_1 CC_1 HASC_1 ISO_1
1 1 USA.44_1 USA United States Texas TX|Tex. <NA> State State <NA> US.TX US-TX
2 2 USA.5_1 USA United States California CA|Calif. <NA> State State <NA> US.CA US-CA
3 3 USA.14_1 USA United States Illinois IL|Ill. <NA> State State <NA> US.IL US-IL
4 4 USA.39_1 USA United States Pennsylvania Commonwealth of Pennsylvania|PA <NA> State State <NA> US.PA US-PA
5 5 USA.33_1 USA United States New York NY|N.Y. <NA> State State <NA> US.NY US-NY
and now easy:
> terra::extract(usa, mypoints)$NAME_1
[1] "Texas" "California" "Illinois" "Pennsylvania" "New York"
this is very sensitive ---for example, a point in the Hudson river is not part of NY, but NA.
It is not clear what exactly you are after, but my guess is that you are looking for terra::extract.
Example data
library(terra)
v <- vect(system.file("ex/lux.shp", package="terra"))
pts <- cbind(c(5.90, 6.17), c(49.94, 49.60))
plot(v)
points(pts, col="red", pch=20)
Query the polygons for each point
extract(v, pts)
# id.y ID_1 NAME_1 ID_2 NAME_2 AREA POP
#1 1 1 Diekirch 5 Wiltz 263 16735
#2 2 3 Luxembourg 10 Luxembourg 237 182607