Map in ggplot2 visualization/displaying bug?

Question

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.

enter image description here

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)

Looks like a problem in the data. Maybe in the ordering, maybe not. When I run summary(mapWorld$data) looks like longitude is coded from -179 to 190... I would expect -180 to 180 — Gregor Thomas
– Gregor Thomas, Commented May 20, 2015 at 21:50
I had not thought of that. I will try with other data. Thanks ! — ePoQ
– ePoQ, Commented May 20, 2015 at 21:53
I can replicate your problem, but the examples at the bottom of ?border work just fine for me. I'm 99% sure it's a data issue rather than a ggplot issue. — Gregor Thomas
– Gregor Thomas, Commented May 20, 2015 at 21:59
examples at the bottom of ?borders work fine for me too. That's weird since some peoples use borders("world", ...) without any mention of this problem — ePoQ
– ePoQ, Commented May 20, 2015 at 22:09
Adding +coord_equal to the plot appears to fix the problem. But I am not posting this as an answer because I am not certain it is a solution per se i.e. Shouldn't the projection specification in coord_map() suffice ??? — shekeine
– shekeine, Commented May 25, 2015 at 11:04

Johan Larsson · Accepted Answer · 2016-05-16 10:08:52Z

2

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))

edited May 16, 2016 at 10:08

Johan Larsson

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answered May 28, 2015 at 8:21

ePoQ

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1 Comment

Johan Larsson Over a year ago

This throws me the following error: Error in .clip(polys, xlim, ylim, isPolygons = TRUE, keepExtra) : (list) object cannot be coerced to type 'double'

Erathia · Accepted Answer · 2015-05-26 16:10:58Z

1

why you need to use?

ggplot() + mapWorld +
  coord_map("mercator") +
  ylim(-90,90)

if u use just

ggplot() + mapWorld

It works perfectly

answered May 26, 2015 at 16:10

Erathia

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