tm_scale_continuous: Scales: continuous scale

In tmap: Thematic Maps

Scales: continuous scale

Description

Scales in tmap are configured by the family of functions with prefix tm_scale. Such function should be used for the input of the .scale arguments in the layer functions (e.g. fill.scale in tm_polygons()). The function tm_scale_continuous() is used for continuous data. The functions ⁠tm_scale_continuous_<x>()⁠ use transformation functions x.

Usage

tm_scale_continuous(
  n = NULL,
  limits = NULL,
  outliers.trunc = NULL,
  ticks = NULL,
  trans = NULL,
  midpoint = NULL,
  values = NA,
  values.repeat = FALSE,
  values.range = NA,
  values.scale = NA,
  value.na = NA,
  value.null = NA,
  value.neutral = NA,
  labels = NULL,
  label.na = NA,
  label.null = NA,
  label.format = list(),
  trans.args = list()
)

tm_scale_continuous_log(..., base = exp(1))

tm_scale_continuous_log2(...)

tm_scale_continuous_log10(...)

tm_scale_continuous_log1p(...)

tm_scale_continuous_sqrt(...)

tm_scale_continuous_pseudo_log(..., base = exp(1), sigma = 1)

Arguments

n	Preferred number of tick labels. Only used if ticks is not specified
limits	Limits of the data values that are mapped to the continuous scale. When NA, the range of data values is taken. When only one value is provided, the range of data values with this provided value is taken. The default depends on the visual variable: it is 0 for all visual variables other than color when tm_scale_continuous is used. For the transformation scale functions, it is NA.
outliers.trunc	Should outliers be truncated? An outlier is a data value that is below or above the respectively lower and upper limit. A logical vector of two values is expected. The first and second value determines whether values lower than the lower limit respectively higher than the upper limit are truncated to the lower respectively upper limit. If FALSE (default), they are considered as missing values.
ticks	Tick values. If not specified, it is determined automatically with n
trans	Transformation function. One of "identity" (default), "log", and "log1p". Note: the base of the log scale is irrelevant, since the log transformed values are normalized before mapping to visual values.
midpoint	The data value that is interpreted as the midpoint. By default it is set to 0 if negative and positive values are present. Useful when values are diverging colors. In that case, the two sides of the color palette are assigned to negative respectively positive values. If all values are positive or all values are negative, then the midpoint is set to NA, which means that the value that corresponds to the middle color class (see style) is mapped to the middle color. If it is specified for sequential color palettes (e.g. "Blues"), then this color palette will be treated as a diverging color palette.
values	(generic scale argument) The visual values. For colors (e.g. fill or col for tm_polygons()) this is a palette name from the cols4all package (see cols4all::c4a()) or vector of colors, for size (e.g. size for tm_symbols()) these are a set of sizes (if two values are specified they are interpret as range), for symbol shapes (e.g. shape for tm_symbols()) these are a set of symbols, etc. The tmap option values.var contains the default values per visual variable and in some cases also per data type.
values.repeat	(generic scale argument) Should the values be repeated in case there are more categories?
values.range	(generic scale argument) Range of the values, especially useful for color palettes. Vector of two numbers (both between 0 and 1) where the first determines the minimum and the second the maximum. Full range, which means that all values are used, is encoded as c(0, 1). For instance, when a gray scale is used for color (from black to white), c(0,1) means that all colors are used, ⁠0.25, 0.75⁠ means that only colors from dark gray to light gray are used (more precisely "grey25" to "grey75"), and ⁠0, 0.5⁠ means that only colors are used from black to middle gray ("grey50"). When only one number is specified, this is interpreted as the second number (where the first is set to 0). Default values can be set via the tmap option values.range.
values.scale	(generic scale argument) Scaling of the values. Only useful for size-related visual variables, such as size of tm_symbols() and lwd of tm_lines().
value.na	(generic scale argument) Value used for missing values. See tmap option "value.na" for defaults per visual variable.
value.null	(generic scale argument) Value used for NULL values. See tmap option "value.null" for defaults per visual variable. Null data values occur when out-of-scope features are shown (e.g. for a map of Europe showing a data variable per country, the null values are applied to countries outside Europe).
value.neutral	(generic scale argument) Value that can be considered neutral. This is used for legends of other visual variables of the same map layer. E.g. when both fill and size are used for tm_symbols() (using filled circles), the size legend items are filled with the value.neutral color from the fill.scale scale, and fill legend items are bubbles of size value.neutral from the size.scale scale.
labels	(generic scale argument) Labels
label.na	(generic scale argument) Label for missing values
label.null	(generic scale argument) Label for null (out-of-scope) values
label.format	(generic scale argument) Label formatting (similar to legend.format in tmap3)
trans.args	list of additional argument for the transformation (generic transformation arguments)
...	passed on to tm_scale_continuous()
base	base of logarithm
sigma	Scaling factor for the linear part of pseudo-log transformation.

See Also

tm_scale()

Examples

tm_shape(World) +
  tm_polygons(
  	fill = "HPI",
    fill.scale = tm_scale_continuous(values = "scico.roma", midpoint = 30))

tm_shape(metro) +
  tm_bubbles(
  	size = "pop1950", 
    size.scale = tm_scale_continuous(
      values.scale = 1),
    size.legend = tm_legend("Population in 1950", frame = FALSE))

tm_shape(metro) +
  tm_bubbles(
    size = "pop1950", 
    size.scale = tm_scale_continuous(
      values.scale = 2, 
      limits = c(0, 12e6), 
      ticks = c(1e5, 3e5, 8e5, 4e6, 1e7), 
      labels = c("0 - 200,000", "200,000 - 500,000", "500,000 - 1,000,000", 
        "1,000,000 - 10,000,000", "10,000,000 or more"), 
      outliers.trunc = c(TRUE, TRUE)),
    size.legend = tm_legend("Population in 1950", frame = FALSE))
# Note that for this type of legend, we recommend tm_scale_intervals()

tmap documentation built on April 4, 2025, 2:05 a.m.