geom_tissot: Add Tissot's indicatrix to a map

In crstools: Tools to Work with Projections

Add Tissot's indicatrix to a map

Description

This function adds Tissot's indicatrix to a map. Tissot's indicatrix is a mathematical contrivance used in cartography to characterize local distortions due to map projection.

Usage

geom_tissot(
  mapping = ggplot2::aes(),
  data = NULL,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE,
  centres = c(5, 5),
  radius = NULL,
  fill = "red",
  alpha = 0.7,
  ...
)

Arguments

mapping	Set of aesthetic mappings created by ggplot2::aes(). If specified and inherit.aes = TRUE (the default), it is combined with the default mapping at the top level of the plot. You must supply mapping if there is no plot mapping.
data	The data to be displayed in this layer. There are two options: A sf object or a SpatRaster object
na.rm	If FALSE, the default, missing values are removed with a warning. If TRUE, missing values are silently removed.
show.legend	logical. Should this layer be included in the legends? NA, the default, includes if any aesthetics are mapped. FALSE never includes, and TRUE always includes. It can also be a named logical vector to finely select the aesthetics to display.
inherit.aes	If FALSE, overrides the default aesthetics, rather than combining with them. This is most useful for helper functions that define both data and aesthetics and shouldn't inherit behaviour from the default plot specification, e.g. ggplot2::geom_point().
centres	Either a list with elements "lng" and "lat" giving the longitudes and latitudes of the grid of centres for the Tissot's indicatrix, or a vector of length 2 with the number of rows and columns to generate such a grid automatically. The latter is passed to pretty() to get pretty breaks, and the exact number of Tissot's circles might differ from the input numbers (see pretty() for details. It defaults to c(5,5).
radius	The radius of the circles (see sf::st_buffer() for an explanation of how units are created; we recommend that you explicitly state your using with the units::as_units(), e.g units::as_units(100, "km")
fill	The fill colour of the circles
alpha	The transparency of the circles
...	Other arguments passed on to ggplot2::geom_sf()

Value

A ggplot2 object

Examples

# load required packages
library(rnaturalearth)
library(sf)
library(ggplot2)
s_america_sf <- ne_countries(continent = "South America", returnclass = "sf")
s_am_equal_area <- suggest_crs(s_america_sf, distortion = "equal_area")
ggplot(data = s_america_sf) +
 geom_sf() +
 geom_tissot() +
 coord_sf(crs = s_am_equal_area$proj4) +
 theme_minimal()

crstools documentation built on March 19, 2026, 5:08 p.m.