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rggplot2mapspolygonggmap

Plot a small region of a map with ocean in ggplot2

I am trying to plot some parts of Canada using the ggplot2 package. I know that it could be tricky to keep the entire polygons because ggplot is getting rid of the points outside the limits (if you use limits in scale_x/y_continuous()). To overcome this, it is useful to plot the entire map and then to apply a zoom (coord_map). My polygons are all okay except that ocean is in the same color than Canada/Alaska. However, if I look at the entire map it is white.

A working example :

require(rgdal)
require(ggplot2)
YK <- map_data("world")  ##World

## Regions Canada
library(autoimage)
data(canada)
library(broom)
canada_df <- tidy(canada)


p <- (ggplot() 
      + theme_bw()
      + geom_polygon(data = YK, aes(x=long, y = lat, group = group), fill="gray70")
      + geom_path(data = canada_df, aes(x=long, y=lat, group=group), colour="black"))
p

This gives a correct world map : World

Then if I want to zoom at the west part of Canada :

p <- (ggplot() 
      + theme_bw()
      + geom_polygon(data = YK, aes(x=long, y = lat, group = group), fill="gray70")
      + geom_path(data = canada_df, aes(x=long, y=lat, group=group), colour="black")
      + coord_map("mercator", xlim=c(-150, -120), ylim=c(50, 70)))
p

This gives :

1

Regions are correct but the Pacific ocean should be in white in the left side... So I tried with the other way :

p <- (ggplot() 
      + theme_bw()
      + geom_polygon(data = YK, aes(x=long, y = lat, group = group), fill="gray70")
      + geom_path(data = canada_df, aes(x=long, y=lat, group=group), colour="black")
      + scale_x_continuous(limits = c(-150, -120))
      + scale_y_continuous(limits = c(50, 70)))
p

Which gives :

2

The ocean is in white but as excepted, the polygons are cropped...

Is there a way to have this zoom with the entire polygons and the ocean in white ? Because like this, it is as if everything was the continent...

Thank you !

Solution

  • Seems the problem is with coord_map. If using coord_cartesian or coord_fixed the zoom in is ok. And coord_quickmap works too.

    p <- ggplot() +
      theme_bw() +
      geom_polygon(data = YK, aes(x=long, y = lat, group = group), fill="gray70") +
      geom_path(data = canada_df, aes(x=long, y=lat, group=group), colour="black")
p

p + coord_cartesian(xlim=c(-150, -120), ylim=c(50, 70))

p + coord_fixed(ratio = 2, xlim=c(-150, -120), ylim=c(50, 70))


p + coord_quickmap(xlim=c(-150, -120), ylim=c(50, 70))