Produce labelled contour lines in ggplot2

Contour lines are available already in ggplot2, but the native geom_contour does not allow the lines to be labelled with the level of each contour. geom_textcontour adds this ability.

Usage

geom_textcontour(
  mapping = NULL,
  data = NULL,
  stat = "textcontour",
  position = "identity",
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE,
  lineend = "butt",
  linejoin = "round",
  linemitre = 10,
  bins = NULL,
  binwidth = NULL,
  breaks = NULL,
  ...
)

geom_labelcontour(
  mapping = NULL,
  data = NULL,
  stat = "textcontour",
  position = "identity",
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE,
  ...,
  lineend = "butt",
  linejoin = "round",
  linemitre = 10,
  bins = NULL,
  binwidth = NULL,
  breaks = NULL,
  label.padding = unit(0.25, "lines"),
  label.r = unit(0.15, "lines"),
  arrow = NULL
)

stat_textcontour(
  mapping = NULL,
  data = NULL,
  geom = "textcontour",
  position = "identity",
  ...,
  bins = NULL,
  binwidth = NULL,
  breaks = NULL,
  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. 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. borders().

lineend

Line end style (round, butt, square).

linejoin

Line join style (round, mitre, bevel).

linemitre

Line mitre limit (number greater than 1).

bins

Number of contour bins. Overridden by binwidth.

binwidth

The width of the contour bins. Overridden by breaks.

breaks

Numeric vector to set the contour breaks. Overrides binwidth and bins. By default, this is a vector of length ten with pretty() breaks.

...

Other arguments passed on to layer. These are often aesthetics, used to set an aesthetic to a fixed value, like colour = "red" or size = 3. These can also be the following text-path parameters:

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.

arrow

Arrow specification, as created by grid::arrow().

geom

The geometric object to use display the data

Value

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

Aesthetics

geom_textcontour() understands the following aesthetics (required aesthetics are in bold):

x
y
alpha
angle
colour
family
fontface
group
hjust
linecolour
lineheight
linetype
linewidth
size
spacing
textcolour
vjust

In addition to aforementioned aesthetics, geom_labelcontour() also understands:

boxcolour
boxlinetype
boxlinewidth
fill

The spacing aesthetic allows fine control of spacing of text, which is called 'tracking' in typography. The default is 0 and units are measured in 1/1000 em. Numbers greater than zero increase the spacing, whereas negative numbers decrease the spacing.

Learn more about setting these aesthetics in vignette("ggplot2-specs").

Computed variables

The variable `level` is a numeric or a factor depending on whether lines or bands are calculated.

`level`: Height of contour. This is a numeric vector that represents bin boundaries.

Examples

df <- expand.grid(x = seq(nrow(volcano)), y = seq(ncol(volcano)))
df$z <- as.vector(volcano)

ggplot(df, aes(x, y, z = z)) +
  geom_contour_filled(bins = 6, alpha = 0.6) +
  geom_textcontour(bins = 6, size = 2.5, padding = unit(0.05, "in")) +
  scale_fill_manual(values = terrain.colors(11)) +
  theme_classic() +
  theme(legend.position = "none")