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Map annotations: annotation_map

notebooks/annotation_map.livemd

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Map annotations: annotation_map

Mix.install([
  {:giggly, path: Path.join(__DIR__, "..")},
  {:kino, "~> 0.19"}
  ])

About this notebook

This notebook follows the examples on ggplot2's reference page for annotation_map(), in the order the page gives them. Each example shows ggplot2's code first and then Giggly's. An example Giggly cannot draw yet keeps its ggplot2 code and names what it is waiting for, so the page is also a list of what remains.

annotation_map() draws a fixed map on a plot: the outlines in a data frame such as map_data() returns, with a fill and colour of their own. It predates geom_sf() and does not read sf geometry, but it can be drawn alongside geom_sf() layers, or in coord_sf(), which projects it. Giggly has none of it yet.

Cities on a state map

The page's examples run only when the maps package is installed, and the last two only when the sf package is too: each if opens a brace that closes after the last example.

if (requireNamespace("maps", quietly = TRUE)) {
# location of cities in North Carolina
df <- data.frame(
  name = c("Charlotte", "Raleigh", "Greensboro"),
  lat = c(35.227, 35.772, 36.073),
  long = c(-80.843, -78.639, -79.792)
)

p <- ggplot(df, aes(x = long, y = lat)) +
  annotation_map(
    map_data("state"),
    fill = "antiquewhite", colour = "darkgrey"
  ) +
  geom_point(color = "blue") +
  geom_text(
    aes(label = name),
    hjust = 1.105, vjust = 1.05, color = "blue"
  )

# use without coord_sf() is possible but not recommended
p + xlim(-84, -76) + ylim(34, 37.2)

Not in Giggly yet: map data from the maps package and annotation_map().

A projected map

if (requireNamespace("sf", quietly = TRUE)) {
# use with coord_sf() for appropriate projection
p +
  coord_sf(
    crs = sf::st_crs(3347),
    default_crs = sf::st_crs(4326),  # data is provided as long-lat
    xlim = c(-84, -76),
    ylim = c(34, 37.2)
  )

Not in Giggly yet: everything p needs (map data from the maps package and annotation_map()), and coord_sf(), with coordinate reference systems from the sf package.

Mixing with sf layers

# you can mix annotation_map() and geom_sf()
nc <- sf::st_read(system.file("shape/nc.shp", package = "sf"), quiet = TRUE)
p +
  geom_sf(
    data = nc, inherit.aes = FALSE,
    fill = NA, color = "black", linewidth = 0.1
  ) +
  coord_sf(crs = sf::st_crs(3347), default_crs = sf::st_crs(4326))
}}

sf::st_read() reads North Carolina's counties from a file that comes with the sf package.

Not in Giggly yet: everything p needs (map data from the maps package and annotation_map()), sf objects, geom_sf() as a layer that ignores the plot's mapping, and coord_sf().

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