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Ggplot2 plots polygons with wrong topologies


I'm trying to plot polygons in R usingggplot2. In GRASS, QGIS and normal R the map renders fine, butggplot2seems to have some kind of topological difficultes I can't explain. With normal R it looks like this:

library(rgdal) library(ggplot2) regions <- readOGR(dir, layer) plot(regions)

And withggplot2:

ggplot() + geom_polygon(data=regions, aes(long, lat))

To add to the confusion,gplot2is connecting polygons that have absolutely nothing to do with each other - Iceland to Ireland, for instance. How can I fix the plot?


A group aesthetic is missing:

ggplot() + geom_polygon(data=fortify(regions), aes(long, lat, group=group))

Otherwise the last point of a polygon is connected with the first point of the next polygon.

See also here: