ggpolar: Nicely formatted polar ggplot

In EarthSystemDiagnostics/grfxtools: An R package of tools to assist with various plotting tasks

Nicely formatted polar ggplot

Description

Produce nicely formatted maps of the Arctic or Antarctic in polar projection. Also works for longitudinal segments, e.g. just Greenland.

Usage

ggpolar(
  pole = c("N", "S"),
  data.layer = NULL,
  max.lat,
  min.lat,
  max.lon = 180,
  min.lon = -180,
  longitude.spacing = 60,
  n.lat.labels = 4,
  plot.political.boundaries = FALSE,
  land.fill.colour = "Grey",
  land.outline.colour = "Black",
  rotate = FALSE,
  nearest.x.degrees = 5,
  lat.ax.vals = NULL,
  long.ax.vals = NULL,
  plt.lat.axes = TRUE,
  plt.lat.labels = plt.lat.axes,
  plt.lon.axes = TRUE,
  plt.lon.labels = plt.lon.axes,
  f.long.label.ticks = 20,
  f.long.label.pos = 7,
  rotate.long.labels = TRUE,
  lat.ax.labs.pos = NULL,
  ax.labs.size = 4,
  size = 0.5,
  size.axes = 0.25,
  size.outer = 1,
  clip = "on"
)

Arguments

pole	character; which pole: north ("N") or south ("S")? Note that full-longitude south polar plots only include the Antarctic main land, irrespective of the latitude setting.
data.layer	optional ggplot2 layer of data onto which the polar map shall be plotted. Defaults to NULL which only plots the map.
max.lat	maximum latitude in degree.
min.lat	minimum latitude in degree.
max.lon	maximum longitude in degree.
min.lon	minimum longitude in degree.
longitude.spacing	interval between longitude axis tick marks.
n.lat.labels	approximate number of latitude tick marks.
plot.political.boundaries	logical; should political (country) boundaries be plotted? Defaults to FALSE.
land.fill.colour	colour to shade the land (default "Grey").
land.outline.colour	colour for the land surface outlines (default "Black"); set to the same colour as land.fill.colour to hide them. This parameter also controls the colours of the political boundaries, if they are switched on.
rotate	logical; if plotting a segment of < 360 degrees longitude, rotate the plot so that north is up (or south is down) as seen from the mean longitude of the segment.
nearest.x.degrees	round latitude tickmarks to how many degrees?
lat.ax.vals	manually set the latitude axis values where to plot latitude labels and lines. This overrides the automatic setting by n.lat.labels and x.nearest.degress, while the default NULL means to use the automatic setting.
long.ax.vals	manually set the longitude axis values where to plot longitude labels and lines. This overrides the automatic setting by longitude.spacing, while the default NULL means to use the automatic setting.
plt.lat.axes	logical; shall latitude axes be plotted?
plt.lat.labels	logical; shall latitude labels be plotted? Per default set to the value of plt.lat.axes.
plt.lon.axes	logical; shall longitude axes be plotted?
plt.lon.labels	logical; shall longitude labels be plotted? Per default set to the value of plt.lon.axes.
f.long.label.ticks	fraction of the plotted latitude axis range by which the longitude ticksmarks extend behind the outer latitude axis, i.e. the minimum (maximum) latitude for north (south) polar plots.
f.long.label.pos	fraction of the plotted latitude axis range by which the longitude labels are offset from the outer latitude axis.
rotate.long.labels	logical; controls whether the longitude axis labels are rotated according to their value and the setting of rotate (the default) or not.
lat.ax.labs.pos	longitudinal positions of the latitude axis labels. Per default, the labels are placed at 0 E (180 W) for north (south) polar plots or at the mean longitude of a segment; use this parameter to override the default setting.
ax.labs.size	size in mm of latitude and longitude axis labels.
size	size in mm of the continental and land outlines.
size.axes	size in mm of the latitude and longitude axes.
size.outer	size in mm of the outer (and potential inner) longitude circle and, if plotting a segment, of the outer latitude lines.
clip	Should drawing be clipped to the extent of the plot panel? A setting of "on" (the default) means yes, and a setting of "off" means no. For details, please see coord_cartesian.

Author(s)

Andrew Dolman <[e-mail]> with some modifications by Thomas Münch.

Source

Code adapted from Mikey Harper's plot; see https://stackoverflow.com/a/49084793.

Coastlines and political boundaries for complete north polar plots, and for north and south polar segment plots, have been obtained from the rnaturalearth package: https://cran.r-project.org/web/packages/rnaturalearth/index.html

Complete south polar plots use ggplot2 data.

Examples

# full north polar plot
ggpolar(pole = "N", max.lat = 90, min.lat = 55, n.lat.labels = 4)

# with political boundaries
ggpolar(pole = "N", max.lat = 90, min.lat = 55, n.lat.labels = 4,
        plot.political.boundaries = TRUE)

# hide land surface outlines
ggpolar(pole = "N", max.lat = 90, min.lat = 55, n.lat.labels = 4,
        land.outline.colour = "Grey")

# full south polar plot
ggpolar(pole = "S", max.lat = -60, min.lat = -90)

# north polar segment plot with adjusted longitude and latitude labelling
ggpolar(pole = "N", max.lat = 90, min.lat = 55,
        max.lon = 0, min.lon = -80,
        longitude.spacing = 15, n.lat.labels = 5)

# rotate the segment
ggpolar(pole = "N", max.lat = 90, min.lat = 55,
        max.lon = 0, min.lon = -80,
        longitude.spacing = 15, n.lat.labels = 5,
        rotate = TRUE)

# south polar segment plot
ggpolar(pole = "S", max.lat = -55, min.lat = -90,
        max.lon = 80, min.lon = -20,
        longitude.spacing = 30, rotate = TRUE)

# it is also possible to plot a ring segment;
# additionally, there are various options to cuzstomize position and look of
# axis labels etc., with a few examples shown here
ggpolar(pole = "N", max.lat = 85, min.lat = 57.5,
  max.lon = -10, min.lon = -75, rotate = TRUE,
  lat.ax.vals = c(60, 70, 80),   # explicitly specify latitude labels
  long.ax.vals = -c(20, 40, 60), # explicitly specify longitude labels
  f.long.label.ticks = Inf,      # don't draw longitude lines beyond segment
  f.long.label.pos = 15,         # adjust label position from segment outline
  rotate.long.labels = FALSE,    # don't rotate longitude labels
  lat.ax.labs.pos = -75 - c(3.5, 5, 10), # move latitude labels to left side
  ax.labs.size = 4.75)                   # larger labels

# ---------------------------------------------------------------------------

# if you want to add points or a spatial field of data to a ggpolar plot, it
# can be convenient to create that plot separately and then provide it as an
# argument to ggpolar, so that it can be added to the polar plot internally:

library(ggplot2)

# create some dummy data
nx <- 360 / 5
ny <- 30 / 5

lon <- seq(0, 355, length.out = nx)
lat <- seq(-65, -90, length.out = ny)

df <- data.frame(lon = rep(lon, times = ny), lat = rep(lat, each = nx),
                 dat = runif(n = nx * ny, min = -1, max = 1))

# Colorbrewer2 colour scales for plotting the "correlation" data can be
# obtained directly with the respective grfxtools function
colour.scale <- ColorPal("RdBu", rev = TRUE)

# create ggplot for data
p <- ggplot() +
  geom_tile(aes(x = lon, y = lat, fill = dat),
            data = df, colour = "transparent") +
  scale_fill_gradientn(colours = colour.scale,
                       limits = c(-1, 1),
                       name = "Correlation") +
  theme(legend.key.height = unit(0.75, units = "inches"),
        legend.text = element_text(size = 18),
        legend.title = element_text(size = 18),
        text = element_text(size = 18))

# plot data projected on south polar map
ggpolar(pole = "S", data.layer = p,
        max.lat = -60, min.lat = -90, n.lat.labels = 3,
        longitude.spacing = 45,
        land.fill.colour = "transparent")

# ---------------------------------------------------------------------------

## Not run: 
ggpolar(pole = "W", max.lat = -55, min.lat = -90)
ggpolar(pole = "S", max.lat = 90, min.lat = 55)
ggpolar(pole = "S", max.lat = -90, min.lat = -55)

## End(Not run)

EarthSystemDiagnostics/grfxtools documentation built on Aug. 5, 2023, 1:43 p.m.