geom_spat_contour: Plot 'SpatRaster' contours

In tidyterra: 'tidyverse' Methods and 'ggplot2' Helpers for 'terra' Objects

Plot SpatRaster contours

Description

These geoms create contours of SpatRaster objects. To specify a valid surface, you should specify the layer on aes(z = layer_name), otherwise all the layers would be consider for creating contours. See also Facets section.

The underlying implementation is based on ggplot2::geom_contour().

geom_spatraster_contour_text() creates labeled contours and it is implemented on top of isoband::isolines_grob().

Usage

geom_spatraster_contour(
  mapping = NULL,
  data,
  ...,
  maxcell = 5e+05,
  bins = NULL,
  binwidth = NULL,
  breaks = NULL,
  na.rm = TRUE,
  show.legend = NA,
  inherit.aes = TRUE,
  mask_projection = FALSE
)

geom_spatraster_contour_text(
  mapping = NULL,
  data,
  ...,
  maxcell = 5e+05,
  bins = NULL,
  binwidth = NULL,
  breaks = NULL,
  size.unit = "mm",
  label_format = scales::label_number(),
  label_placer = isoband::label_placer_minmax(),
  na.rm = TRUE,
  show.legend = NA,
  inherit.aes = TRUE,
  mask_projection = FALSE
)

geom_spatraster_contour_filled(
  mapping = NULL,
  data,
  ...,
  maxcell = 5e+05,
  bins = NULL,
  binwidth = NULL,
  breaks = NULL,
  na.rm = TRUE,
  show.legend = NA,
  inherit.aes = TRUE,
  mask_projection = FALSE
)

Arguments

mapping	Set of aesthetic mappings created by ggplot2::aes(). See Aesthetics specially in the use of fill aesthetic.
data	A SpatRaster object.
...	Other arguments passed on to layer()'s params argument. These arguments broadly fall into one of 4 categories below. Notably, further arguments to the position argument, or aesthetics that are required can not be passed through .... Unknown arguments that are not part of the 4 categories below are ignored. Static aesthetics that are not mapped to a scale, but are at a fixed value and apply to the layer as a whole. For example, colour = "red" or linewidth = 3. The geom's documentation has an Aesthetics section that lists the available options. The 'required' aesthetics cannot be passed on to the params. Please note that while passing unmapped aesthetics as vectors is technically possible, the order and required length is not guaranteed to be parallel to the input data. When constructing a layer using a ⁠stat_*()⁠ function, the ... argument can be used to pass on parameters to the geom part of the layer. An example of this is stat_density(geom = "area", outline.type = "both"). The geom's documentation lists which parameters it can accept. Inversely, when constructing a layer using a ⁠geom_*()⁠ function, the ... argument can be used to pass on parameters to the stat part of the layer. An example of this is geom_area(stat = "density", adjust = 0.5). The stat's documentation lists which parameters it can accept. The key_glyph argument of layer() may also be passed on through .... This can be one of the functions described as key glyphs, to change the display of the layer in the legend.
maxcell	positive integer. Maximum number of cells to use for the plot.
bins	Number of contour bins. Overridden by breaks.
binwidth	The width of the contour bins. Overridden by bins.
breaks	One of: Numeric vector to set the contour breaks A function that takes the range of the data and binwidth as input and returns breaks as output. A function can be created from a formula (e.g. ~ fullseq(.x, .y)). Overrides binwidth and bins. By default, this is a vector of length ten with pretty() breaks.
na.rm	If TRUE, the default, missing values are silently removed. If FALSE, missing values are removed with a warning.
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.
mask_projection	logical, defaults to FALSE. If TRUE, mask out areas outside the input extent. For example, to avoid data wrapping around the date-line in Equal Area projections. This parameter is passed to terra::project() when reprojecting the SpatRaster.
size.unit	How the size aesthetic is interpreted: as millimetres ("mm", default), points ("pt"), centimetres ("cm"), inches ("in"), or picas ("pc").
label_format	One of: NULL for no labels. This produced the same result than geom_spatraster_contour(). A character vector giving labels (must be same length as the breaks produced by bins, binwidth, or breaks). A function that takes the breaks as input and returns labels as output, as the default setup (scales::label_number()).
label_placer	Function that controls how labels are placed along the isolines. Uses label_placer_minmax() by default.

Value

A ggplot2 layer

terra equivalent

terra::contour()

Aesthetics

geom_spatraster_contour() / geom_spatraster_contour_text() understands the following aesthetics:

• alpha

• colour

• group

• linetype

• linewidth geom_spatraster_contour_text() understands also:

• size

• label

• family

• fontface

Additionally, geom_spatraster_contour_filled() understands also the following aesthetics, as well as the ones listed above:

• fill

• subgroup

Check ggplot2::geom_contour() for more info on contours and vignette("ggplot2-specs", package = "ggplot2") for an overview of the aesthetics.

Computed variables

These geom computes internally some variables that are available for use as aesthetics, using (for example) ⁠aes(color = after_stat(<computed>))⁠ (see ggplot2::after_stat()).

• after_stat(lyr): Name of the layer.

• after_stat(level): Height of contour. For contour lines, this is numeric vector that represents bin boundaries. For contour bands, this is an ordered factor that represents bin ranges.

• after_stat(nlevel): Height of contour, scaled to maximum of 1.

• after_stat(level_low), after_stat(level_high), after_stat(level_mid): (contour bands only) Lower and upper bin boundaries for each band, as well the mid point between the boundaries.

Dropped variables

• z: After contouring, the z values of individual data points are no longer available.

Coords

When the SpatRaster does not present a crs (i.e., terra::crs(rast) == "") the geom does not make any assumption on the scales.

On SpatRaster that have a crs, the geom uses ggplot2::coord_sf() to adjust the scales. That means that also the SpatRaster may be reprojected.

Facets

You can use facet_wrap(~lyr) for creating a faceted plot by each layer of the SpatRaster object. See ggplot2::facet_wrap() for details.

See Also

ggplot2::geom_contour().

The metR package also provides a set of alternative functions:

• metR::geom_contour2().

• metR::geom_text_contour() and metR::geom_label_contour().

• metR::geom_contour_tanaka().

Other ggplot2 utils: autoplot.Spat, fortify.Spat, geom_spatraster(), geom_spatraster_rgb(), ggspatvector, stat_spat_coordinates()

Examples

library(terra)

# Raster
f <- system.file("extdata/volcano2.tif", package = "tidyterra")
r <- rast(f)

library(ggplot2)

ggplot() +
  geom_spatraster_contour(data = r)


# Labelled
ggplot() +
  geom_spatraster_contour_text(
    data = r, breaks = c(110, 130, 160, 190),
    color = "grey10", family = "serif"
  )


ggplot() +
  geom_spatraster_contour(
    data = r, aes(color = after_stat(level)),
    binwidth = 1,
    linewidth = 0.4
  ) +
  scale_color_gradientn(
    colours = hcl.colors(20, "Inferno"),
    guide = guide_coloursteps()
  ) +
  theme_minimal()

# Filled with breaks
ggplot() +
  geom_spatraster_contour_filled(data = r, breaks = seq(80, 200, 10)) +
  scale_fill_hypso_d()

# Both lines and contours
ggplot() +
  geom_spatraster_contour_filled(
    data = r, breaks = seq(80, 200, 10),
    alpha = .7
  ) +
  geom_spatraster_contour(
    data = r, breaks = seq(80, 200, 2.5),
    color = "grey30",
    linewidth = 0.1
  ) +
  scale_fill_hypso_d()

tidyterra documentation built on April 15, 2025, 1:15 a.m.