Rafael Martins Rafael Martins -4 years ago 56
R Question

map.where returning NA

Why isn't map.where finding the right county for this GPS coordinate?

> maps::map.where('county', y = 47.9078 , x = -122.2803)
[1] NA


It works for other points in Washington.

> maps::map.where('county', y = 46.0900, x = -121.7600)
[1] "washington,skamania"

Answer Source

I you look in detail, you will see the point in fact falls just outside all polygons:

> maps::map('county',xlim=c(-123,-122),ylim=c(47,48),fill=TRUE)
> points( y =  47.9078 , x = -122.2803,col=2)

enter image description here So the NA result is normal in that respect. It may of course be wrong due to the limited resolution of the county map. Clearly the point is very close to or on the coast, and maybe a better quality map may give a different result. Using rnaturalearth you can make a similar plot, which clearly shows the difference:

library(rnaturalearth)
cc=ne_states(iso_a2="US")
maps::map(cc,xlim=c(-123,-122),ylim=c(47,48),fill=TRUE)
points( y =  47.9078 , x = -122.2803,col=2)
maps::map('county',xlim=c(-123,-122),ylim=c(47,48),add=TRUE,col=3)

enter image description here

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