Skip to contents

Visualise sf objects with labels

Source: R/geom_textsf.R
geom_textsf.Rd

This set of geom, stat, and coord are used to visualise simple feature (sf) objects. For simple plots, you will only need geom_sf() as it uses stat_sf() and adds coord_sf() for you. geom_textsf() is an unusual geom because it will draw different geometric objects depending on what simple features are present in the data: you can get points, lines, or polygons.

Usage

geom_textsf(
  mapping = aes(),
  data = NULL,
  stat = "sf",
  position = "identity",
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE,
  ...
)

geom_labelsf(
  mapping = aes(),
  data = NULL,
  stat = "sf",
  position = "identity",
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE,
  ...
)

Arguments

mapping

Set of aesthetic mappings created by aes() or 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 three options:

If NULL, the default, the data is inherited from the plot data as specified in the call to ggplot().

A data.frame, or other object, will override the plot data. All objects will be fortified to produce a data frame. See fortify() for which variables will be created.

A function will be called with a single argument, the plot data. The return value must be a data.frame, and will be used as the layer data. A function can be created from a formula (e.g. ~ head(.x, 10)).

stat

The statistical transformation to use on the data for this layer, as a string.

position

Position adjustment, either as a string, or the result of a call to a position adjustment function.

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.

You can also set this to one of "polygon", "line", and "point" to override the default legend.

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. borders().

...

Arguments passed on to geom_textpath, geom_labelpath

text_only

A logical(1) indicating whether the path part should be plotted along with the text (FALSE, the default). If TRUE, any parameters or aesthetics relating to the drawing of the path will be ignored.

gap

A logical(1) which if TRUE, breaks the path into two sections with a gap on either side of the label. If FALSE, the path is plotted as a whole. Alternatively, if NA, the path will be broken if the string has a vjust between 0 and 1, and not otherwise. The default for the label variant is FALSE and for the text variant is NA.

upright

A logical(1) which if TRUE (default), inverts any text where the majority of letters would upside down along the path, to improve legibility. If FALSE, the path decides the orientation of text.

halign

A character(1) describing how multi-line text should be justified. Can either be "center" (default), "left" or "right".

offset

A unit object of length 1 to determine the offset of the text from the path. If this is NULL (default), the vjust parameter decides the offset. If not NULL, the offset argument overrules the vjust setting.

parse

A logical(1) which if TRUE, will coerce the labels into expressions, allowing for plotmath syntax to be used.

straight

A logical(1) which if TRUE, keeps the letters of a label on a straight baseline and if FALSE (default), lets individual letters follow the curve. This might be helpful for noisy paths.

padding

A unit object of length 1 to determine the padding between the text and the path when the gap parameter trims the path.

text_smoothing

a numeric(1) value between 0 and 100 that smooths the text without affecting the line portion of the geom. The default value of 0 means no smoothing is applied.

rich

A logical(1) whether to interpret the text as html/markdown formatted rich text. Default: FALSE. See also the rich text section of the details in geom_textpath().

remove_long

if TRUE, labels that are longer than their associated path will be removed.

label.padding

Amount of padding around label. Defaults to 0.25 lines.

label.r

Radius of rounded corners. Defaults to 0.15 lines.

Value

A Layer ggproto object that can be added to a plot.

Geometry aesthetic

geom_textsf() uses a unique aesthetic: geometry, giving an column of class sfc containing simple features data. There are three ways to supply the geometry aesthetic:

  • Do nothing: by default geom_textsf() assumes it is stored in the geometry column.

  • Explicitly pass an sf object to the data argument. This will use the primary geometry column, no matter what it's called.

  • Supply your own using aes(geometry = my_column)

Unlike other aesthetics, geometry will never be inherited from the plot.

CRS

coord_sf() ensures that all layers use a common CRS. You can either specify it using the crs param, or coord_sf() will take it from the first layer that defines a CRS.

Combining sf layers and regular geoms

Most regular geoms, such as geom_point(), geom_path(), geom_text(), geom_polygon() etc. will work fine with coord_sf(). However when using these geoms, two problems arise. First, what CRS should be used for the x and y coordinates used by these non-sf geoms? The CRS applied to non-sf geoms is set by the default_crs parameter, and it defaults to NULL, which means positions for non-sf geoms are interpreted as projected coordinates in the coordinate system set by the crs parameter. This setting allows you complete control over where exactly items are placed on the plot canvas, but it may require some understanding of how projections work and how to generate data in projected coordinates. As an alternative, you can set default_crs = sf::st_crs(4326), the World Geodetic System 1984 (WGS84). This means that x and y positions are interpreted as longitude and latitude, respectively. You can also specify any other valid CRS as the default CRS for non-sf geoms.

The second problem that arises for non-sf geoms is how straight lines should be interpreted in projected space when default_crs is not set to NULL. The approach coord_sf() takes is to break straight lines into small pieces (i.e., segmentize them) and then transform the pieces into projected coordinates. For the default setting where x and y are interpreted as longitude and latitude, this approach means that horizontal lines follow the parallels and vertical lines follow the meridians. If you need a different approach to handling straight lines, then you should manually segmentize and project coordinates and generate the plot in projected coordinates.

See also

stat_sf_coordinates(). Other geom layers that place text on paths.

Examples

ggplot(waterways) +
 geom_textsf(label = "Forth and Clyde Canal",
              hjust = 0.62, vjust = -0.3, fill = "#E4E0A3") +
 lims(x = c(-4.2, -3.9), y = c(55.9, 56))
#> Warning: The text offset exceeds the curvature in one or more paths. This will result in
#> displaced letters. Consider reducing the vjust or text size, or use the hjust
#> parameter to move the string to a different point on the path.
#> Warning: The text offset exceeds the curvature in one or more paths. This will result in
#> displaced letters. Consider reducing the vjust or text size, or use the hjust
#> parameter to move the string to a different point on the path.
#> Warning: The text offset exceeds the curvature in one or more paths. This will result in
#> displaced letters. Consider reducing the vjust or text size, or use the hjust
#> parameter to move the string to a different point on the path.
#> Warning: The text offset exceeds the curvature in one or more paths. This will result in
#> displaced letters. Consider reducing the vjust or text size, or use the hjust
#> parameter to move the string to a different point on the path.
#> Warning: The text offset exceeds the curvature in one or more paths. This will result in
#> displaced letters. Consider reducing the vjust or text size, or use the hjust
#> parameter to move the string to a different point on the path.
#> Warning: The text offset exceeds the curvature in one or more paths. This will result in
#> displaced letters. Consider reducing the vjust or text size, or use the hjust
#> parameter to move the string to a different point on the path.
#> Warning: The text offset exceeds the curvature in one or more paths. This will result in
#> displaced letters. Consider reducing the vjust or text size, or use the hjust
#> parameter to move the string to a different point on the path.
#> Warning: The text offset exceeds the curvature in one or more paths. This will result in
#> displaced letters. Consider reducing the vjust or text size, or use the hjust
#> parameter to move the string to a different point on the path.
#> Warning: The text offset exceeds the curvature in one or more paths. This will result in
#> displaced letters. Consider reducing the vjust or text size, or use the hjust
#> parameter to move the string to a different point on the path.
#> Warning: The text offset exceeds the curvature in one or more paths. This will result in
#> displaced letters. Consider reducing the vjust or text size, or use the hjust
#> parameter to move the string to a different point on the path.