[R-sig-Geo] world map problem with Mollweide projection

[Roger Bivand]

On Mon, 6 Nov 2017, Elias T Krainski wrote:

> Dear all,
>
> Anybody knows a easy way how to get rid of those east-west lines at the north 
> in the following plot:
>
> library(maps)
> map('world',, projection='mollweide')

In sp (can be done in sf too, I think):

wrld <- map("world", fill=TRUE, plot=FALSE)
library(sp)
library(maptools)
ID <- sapply(strsplit(wrld$names, ":"), "[", 1L)
wrld_sp <- map2SpatialPolygons(wrld, ID=ID)
proj4string(wrld_sp) <- "+proj=longlat +datum=WGS84"
wrld_sp1 <- nowrapSpatialPolygons(wrld_sp, offset=180)
library(rgdal)
wrld_moll <- spTransform(wrld_sp1, CRS("+proj=moll"))
plot(wrld_moll)

The lines or polygons crossing 180 degrees need to be broken into two 
parts at 180 +/- eps; that isn't easy in the maps package.

Roger

>
> best regards,
>
> Elias
>
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-- 
Roger Bivand
Department of Economics, Norwegian School of Economics,
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Editor-in-Chief of The R Journal, https://journal.r-project.org/index.html
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