Coordinates of simple features: stat_sf_coordinates

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

About this notebook

This notebook follows the examples on ggplot2's reference page for stat_sf_coordinates(), 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.

stat_sf_coordinates() reduces each geometry of an sf object, from R's sf package, to one point, by default a point on its surface, and gives that point's coordinates as x and y. Text and labels need exactly one position for each geometry, so geom_sf_text() and geom_sf_label() place theirs with it. Giggly has none of it yet: it has no sf objects.

A point in each county

The examples read the counties of North Carolina from a shapefile that comes with the sf package, and run only where that package is installed.

if (requireNamespace("sf", quietly = TRUE)) {
nc <- sf::st_read(system.file("shape/nc.shp", package="sf"))

ggplot(nc) +
  stat_sf_coordinates()

Not in Giggly yet: sf objects and stat_sf_coordinates().

Error bars at each county

ggplot(nc) +
  geom_errorbarh(
    aes(geometry = geometry,
        xmin = after_stat(x) - 0.1,
        xmax = after_stat(x) + 0.1,
        y = after_stat(y),
        height = 0.04),
    stat = "sf_coordinates"
  )
}

The error bars take their positions from the coordinates the stat computes, through after_stat().

Not in Giggly yet: sf objects, stat_sf_coordinates() given to a geom as stat = "sf_coordinates", horizontal error bars, geom_errorbarh(), and mapping geometry.