symbolmap

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Graphics Symbol Map

Create a graphics symbol map that associates data values with graphical symbols.

Keywords
hplot, spatial
Usage
symbolmap(…, range = NULL, inputs = NULL)
Arguments

Named arguments specifying the graphical parameters. See Details.

range

Optional. Range of numbers that are mapped. A numeric vector of length 2 giving the minimum and maximum values that will be mapped. Incompatible with inputs.

inputs

Optional. A vector containing all the data values that will be mapped to symbols. Incompatible with range.

Details

A graphical symbol map is an association between data values and graphical symbols. The command symbolmap creates an object of class "symbolmap" that represents a graphical symbol map.

Once a symbol map has been created, it can be applied to any suitable data to generate a plot of those data. This makes it easy to ensure that the same symbol map is used in two different plots. The symbol map can be plotted as a legend to the plots, and can also be plotted in its own right.

The possible values of data that will be mapped are specified by range or inputs.

  • if range is given, it should be a numeric vector of length 2 giving the minimum and maximum values of the range of numbers that will be mapped. These limits must be finite.

  • if inputs is given, it should be a vector of any atomic type (e.g. numeric, character, logical, factor). This vector contains all the possible data values that will be mapped.

  • If neither range nor inputs is given, it is assumed that the possible values are real numbers.

The association of data values with graphical symbols is specified by the other arguments which are given in name=value form. These arguments specify the kinds of symbols that will be used, the sizes of the symbols, and graphics parameters for drawing the symbols.

Each graphics parameter can be either a single value, for example shape="circles", or a function(x) which determines the value of the graphics parameter as a function of the data x, for example shape=function(x) ifelse(x > 0, "circles", "squares"). Colourmaps (see colourmap) are also acceptable because they are functions.

Currently recognised graphics parameters, and their allowed values, are:

shape

The shape of the symbol: currently either "circles", "squares", "arrows" or NA. This parameter takes precedence over pch.

size

The size of the symbol: a positive number or zero.

pch

Graphics character code: a positive integer, or a single character. See par.

cex

Graphics character expansion factor.

cols

Colour of plotting characters.

fg,bg

Colour of foreground (or symbol border) and background (or symbol interior).

col,lwd,lty

Colour, width and style of lines.

etch

Logical. If TRUE, each symbol is surrounded by a border drawn in the opposite colour, which improves its visibility against the background. Default is FALSE.

direction,headlength,headangle,arrowtype

Numeric parameters of arrow symbols, applicable when shape="arrows". Here direction is the direction of the arrow in degrees anticlockwise from the \(x\) axis; headlength is the length of the head of the arrow in coordinate units; headangle is the angle subtended by the point of the arrow; and arrowtype is an integer code specifying which ends of the shaft have arrowheads attached (0 means no arrowheads, 1 is an arrowhead at the start of the shaft, 2 is an arrowhead at the end of the shaft, and 3 is arrowheads at both ends).

A vector of colour values is also acceptable for the arguments col,cols,fg,bg if range is specified.

Value

An object of class "symbolmap".

See Also

plot.symbolmap to plot the symbol map itself.

invoke.symbolmap to apply the symbol map to some data and plot the resulting symbols.

update.symbolmap to change the symbol map.

Aliases
  • symbolmap
Examples
# NOT RUN {
  g <- symbolmap(inputs=letters[1:10], pch=11:20)

  g1 <- symbolmap(range=c(0,100), size=function(x) x/50)

  g2 <- symbolmap(shape=function(x) ifelse(x > 0, "circles", "squares"),
                    size=function(x) sqrt(ifelse(x > 0, x/pi, -x)),
                    bg = function(x) ifelse(abs(x) < 1, "red", "black"))

  colmap <- colourmap(topo.colors(20), range=c(0,10))
  g3 <- symbolmap(pch=21, bg=colmap, range=c(0,10))
  plot(g3)
# }
Documentation reproduced from package spatstat, version 1.55-1, License: GPL (>= 2)

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