Q:

Map in ggplot2 visualization/displaying bug?

As you can see below, there is a weird displaying problem on the maps I made using ggplots. The same problem seems to happen with any projection. 

Here is the code:
Only the packages maps and ggplot2 are needed  
  mapWorld <- borders("world", colour="gray50", fill="black")
    ggplot() + mapWorld +
      coord_map("mercator") +
      ylim(-90,90)

A:

Apparently the problem is caused by the polygons that cross the 0 coordinate, the place in which the world merges. R dont knows how to close those polygons and projects them all around the world.
This method recreates the polygons and prevents them from crossing the 0 coordinate (xlim and ylim). It works with any kind of projection.
require(ggplot2)
require(PBSmapping)
require(data.table)

mapWorld <- map_data("world")
setnames(mapWorld, c("X","Y","PID","POS","region","subregion"))
worldmap = clipPolys(mapWorld, xlim=xlim,ylim=ylim, keepExtra=TRUE)
ggplot() + geom_polygon(data = mapWorld, aes(X,Y,group=PID))

