How to add axis to map in cylindrical equal area projection? Why are the polygon lines at the border stretched out?

0
votes

Goal

  1. Add axis that labels coordinates at 30deg latitude, 60deg longitude.
  2. Fix the polygon lines, around ~west Asia, eastern Europe.

Question 1

  1. I do not know what the scale of the axis is when I specify cylindrical equal area projection. (-180 to 180 is ~ -3.1 to 3.1 and -90 to 90 is ~ 1 to 1?)

Question 2

  1. How can I fix the world map polygon that is distorted around west Asia or eastern Europe? wrap = TRUE fixed most of the polygon issues but that one remains.

Sample

library(mapproj)
library(maps)
# World Map, cylindrical equal area projection
map(database= 'world', 
xlim=c(-180,180), 
ylim=c(-90,90),
projection='cylequalarea',
parameters = 0,
fill=T,
col="#f2f2f2",
bg="white",
lty=1,
lwd=1,
orientation=c(90,0,225),
resolution=0,
wrap=T,
)
# Default axis
map.axes()
# Desired axis
axis(1,
at=c(-120,-60,0,60,120),
labels = c('-120','-60','0','60','-120'),
pos=-90)

Map

enter image description here

1
rmapsmap-projections

1 Answers

0
votes

Here is what works for me:

CylEqAreaMAP <- function(){
  library(mapproj)
  library(maps)
  # World Map, cylindrical equal area projection
  map(database = "world2", 
      regions = ".", 
      exact = FALSE, 
      boundary = FALSE,
      interior = FALSE,
      lty = 0,
      projection='cylequalarea', parameters = 0,
      fill = TRUE, 
      col = '#f2f2f2', 
      plot = TRUE, 
      add = FALSE, 
      namesonly = FALSE,
      xlim = c(0,360), ylim = c(-90,90), 
      wrap = TRUE, 
      resolution = 1,
      type = "l", bg = par("bg"), 
      myborder = 0.01, namefield="name")
  # Desired axis
  ## long
  axis(1,
       at=c(-2.05,-1,0,1,2.05),
       labels = c(parse(text = '60^o*E'),parse(text = '120^o*E'),parse(text = '180^o'),parse(text = '120^o*W'),parse(text =  '60^o*W')),
       lwd.ticks = 1,
       lwd = 0,
       pos = -1.1,
       tck =0.01,
       cex.axis = 0.75
  )
  ## lat
  axis(2,
       at=c(-0.67,-0.33,0,0.33,0.67),
       labels = c(parse(text = '60^o*S'),parse(text = '30^o*S'),parse(text = '0^o'),parse(text = '30^o*N'),parse(text = '60^o*N')),
       las =1,
       lwd =0,
       lwd.ticks = 1,
       tck =0.01,
       cex.axis = 0.75
  )
  # title
  title("Site Locations")
}

The above code creates this map, projection = '' when adding points to plot using mapproject() would have saved me submitting an embarrassing plot. Hopefully this spares someone else some time.

World2 map, cylindrical equal area projection