<Description & Motivation>

Inspiration

• http://rpsychologist.com/working-with-shapefiles-projections-and-world-maps-in-ggplot
• https://stackoverflow.com/questions/10620862/use-different-center-than-the-prime-meridian-in-plotting-a-world-map
• https://gist.github.com/rafapereirabr/9a36c2e5ff04aa285fa3
• https://web.stanford.edu/~cengel/cgi-bin/anthrospace/great-circles-on-a-recentered-worldmap-in-ggplot
• https://rpubs.com/benmschmidt/Recenter
• https://seethedatablog.wordpress.com/2016/12/31/r-shift-centralprime-meridian-of-world-map/
• https://gist.github.com/valentinitnelav/c7598fcfc8e53658f66feea9d3bafb40

Installation

library(devtools)
devtools::install_github("thackl/ggworldmap")

Usage

library(tidyverse)
library(ggworldmap)

# a nice projected map with graticules and degree labels
ggworldmap(proj = "moll", degree = list("light", long_by = 80))

# and short for
proj <- "moll"
ggplot() +
  geom_worldmap(proj = proj, color = "gray90", fill = "gray90") +
  geom_graticule(proj = proj, color = "gray80") +
  geom_gratframe(proj = proj, color = "gray80") +
  geom_degree(proj = proj, color = "gray80", long_by = 80) +
  theme_worldmap_light() +
  coord_equal()

ggsave("img/ggworldplot.png", width = 12, height = 6, type = "cairo")

# Pacific centered map with colored countries
long_0 <- 110
ggworldmap(proj = "ortho", long_0 = long_0, mapping = aes(fill=group),
    long_min = long_0-90, long_max = long_0+90, color = "black",
    show.legend = FALSE, graticule = list("light", color = "grey20"),
    degree = list("light", long_n = 3, color = "grey30", family = "Times New Roman")) +
  scale_fill_distiller(palette = "Pastel2")

ggsave("img/east-asia-countries.png", width = 12, height = 6, type = "cairo")

# The Pacific Ring of Fire
data(volcanic_eruptions)            # load example data
proj <- "robin"                     # Robinson projection
long_0 <- -150                      # Center on Pacific
ve_proj <- volcanic_eruptions %>%
  project(proj, long_0) %>%         # project data
  arrange(desc(VEI))                # and get nice plotting order
# plot projected map and data
ggworldmap(ve_proj, long_0 = long_0, proj = proj) +
  geom_point(aes(size = VEI^4, color = VEI), alpha =.5) +
  scale_color_distiller(palette = "Spectral")

ggsave("img/pacific-ring-of-fire.png", width = 12, height = 6, type = "cairo")

# TODO: Project and Concentrate Data

proj <- "robin" # use Robinson projection
long_0 <- -120  # center on Pacific
lat_min <- -70  # and clip the poles
lat_max <- 70

# get some sample data
data(volcanic_eruptions)
volcanic_eruptions <- volcanic_eruptions %>%
  filter(Year > 1919) %>%          # let's look at last 100 years
  project(proj, long_0)            # and we want our data projected
volcanic_eruptions_decluttered <- volcanic_eruptions %>%
  concentrate(lambda = .2) %>%     # round up close points at a single location
  arrange(Type)                    # and order them nicely for plotting


# set up a plot of the world
gg <- ggplot(mapping = aes(x=long, y=lat)) +
  # ----------------------------------------------------------------------------
  # get a world map, centered on the Pacific, in Robinson projection
  geom_worldmap(proj = proj, long_0 = long_0, lat_min = lat_min,
    lat_max = lat_max, color = "grey90", fill = "grey90") +
  # add some grid lines
  geom_graticule(proj = proj, long_0 = long_0, lat_min = lat_min, lat_max = lat_max,
    long_by = 40, linetype = 1, color = "grey80", size = .5, alpha=.3) +
  # and a grid frame
  geom_graticule(proj = proj, long_0 = long_0, lat_min = lat_min, lat_max = lat_max,
     lat_n = 2, long_n = 2, linetype = 1, color = "grey80", size = 1) +
  # and some grid labels
  geom_degree(proj = proj, long_0 = long_0, lat_min = lat_min, lat_max = lat_max,
    long_by = 40, color = "grey60", size = 3)
  # ----------------------------------------------------------------------------
  # now throw our data on the canvas
  geom_array(aes(color = Type), volcanic_eruptions_decluttered, nrow = 7, spread = 2,
    shape = 19, size = .8, vjust = .5) +
  # original locations with overplotting issues
  geom_point(data = volcanic_eruptions, size = .3, alpha = .5) +
  # ----------------------------------------------------------------------------
  # and finally make things pretty
  ggtitle("Significant Volcanic Eruptions", "of the last 100 years by most common types") +
  # with fixed aspect ratio, but no poles,
  coord_equal(ylim = c(-80, 80)) +
  # an almost void greyish theme,
  theme_light(base_size = 15) + theme(
    panel.grid.major = element_blank(), panel.grid.minor = element_blank(),
    axis.text = element_blank(), axis.ticks = element_blank(), axis.title = element_blank(),
    legend.justification=c(0,1), legend.position=c(.52,.29), legend.text.align=0) +
  # and nice colors
  scale_color_brewer("Eruption types", palette="Dark2") +
  # wrapped in facets
  facet_wrap(~Type, ncol=2, strip.position = "left")