# contour {graphics}

### Description

Create a contour plot, or add contour lines to an existing plot.

### Usage

contour(x, ...) ## S3 method for class 'default': contour((x = seq(0, 1, length.out = nrow(z)), y = seq(0, 1, length.out = ncol(z)), z, nlevels = 10, levels = pretty(zlim, nlevels), labels = NULL, xlim = range(x, finite = TRUE), ylim = range(y, finite = TRUE), zlim = range(z, finite = TRUE), labcex = 0.6, drawlabels = TRUE, method = "flattest", vfont, axes = TRUE, frame.plot = axes, col = par("fg"), lty = par("lty"), lwd = par("lwd"), add = FALSE, ...))

### Arguments

- x, y
- locations of grid lines at which the values in
`z`

are measured. These must be in ascending order. By default, equally spaced values from 0 to 1 are used. If`x`

is a`list`

, its components`x$x`

and`x$y`

are used for`x`

and`y`

, respectively. If the list has component`z`

this is used for`z`

. - z
- a matrix containing the values to be plotted (
`NA`

s are allowed). Note that`x`

can be used instead of`z`

for convenience. - nlevels
- number of contour levels desired
**iff**`levels`

is not supplied. - levels
- numeric vector of levels at which to draw contour lines.
- labels
- a vector giving the labels for the contour lines. If
`NULL`

then the levels are used as labels, otherwise this is coerced by`as.character`

. - labcex
`cex`

for contour labelling. This is an absolute size, not a multiple of`par("cex")`

.- drawlabels
- logical. Contours are labelled if
`TRUE`

. - method
- character string specifying where the labels will be located. Possible values are
`"simple"`

,`"edge"`

and`"flattest"`

(the default). See the ‘Details’ section. - vfont
- if
`NULL`

, the current font family and face are used for the contour labels. If a character vector of length 2 then Hershey vector fonts are used for the contour labels. The first element of the vector selects a typeface and the second element selects a fontindex (see`text`

for more information). The default is`NULL`

on graphics devices with high-quality rotation of text and`c("sans serif", "plain")`

otherwise. - xlim, ylim, zlim
- x-, y- and z-limits for the plot.
- axes, frame.plot
- logical indicating whether axes or a box should be drawn, see
`plot.default`

. - col
- color for the lines drawn.
- lty
- line type for the lines drawn.
- lwd
- line width for the lines drawn.
- add
- logical. If
`TRUE`

, add to a current plot. - ...
- additional arguments to
`plot.window`

,`title`

,`Axis`

and`box`

, typically graphical parameters such as`cex.axis`

.

### Details

`contour`

is a generic function with only a default method in base R.

The methods for positioning the labels on contours are `"simple"`

(draw at the edge of the plot, overlaying the contour line), `"edge"`

(draw at the edge of the plot, embedded in the contour line, with no labels overlapping) and `"flattest"`

(draw on the flattest section of the contour, embedded in the contour line, with no labels overlapping). The second and third may not draw a label on every contour line.

For information about vector fonts, see the help for `text`

and `Hershey`

.

Notice that `contour`

interprets the `z`

matrix as a table of `f(x[i], y[j])`

values, so that the x axis corresponds to row number and the y axis to column number, with column 1 at the bottom, i.e. a 90 degree counter-clockwise rotation of the conventional textual layout.

Alternatively, use `contourplot`

from the lattice package where the `formula`

notation allows to use vectors `x`

, `y`

, and `z`

of the same length.

There is limited control over the axes and frame as arguments `col`

, `lwd`

and `lty`

refer to the contour lines (rather than being general graphical parameters). For more control, add contours to a plot, or add axes and frame to a contour plot.

### References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) *The New S Language*. Wadsworth & Brooks/Cole.

### See Also

`options("max.contour.segments")`

for the maximal complexity of a single contour line.

`contourLines`

, `filled.contour`

for color-filled contours, `contourplot`

(and `levelplot`

) from package lattice. Further, `image`

and the graphics demo which can be invoked as `demo(graphics)`

.

### Examples

require(grDevices) # for colours x <- -6:16 op <- par(mfrow = c(2, 2)) contour(outer(x, x), method = "edge", vfont = c("sans serif", "plain")) z <- outer(x, sqrt(abs(x)), FUN = "/") image(x, x, z) contour(x, x, z, col = "pink", add = TRUE, method = "edge", vfont = c("sans serif", "plain")) contour(x, x, z, ylim = c(1, 6), method = "simple", labcex = 1) contour(x, x, z, ylim = c(-6, 6), nlev = 20, lty = 2, method = "simple") par(op) ## Persian Rug Art: x <- y <- seq(-4*pi, 4*pi, len = 27) r <- sqrt(outer(x^2, y^2, "+")) opar <- par(mfrow = c(2, 2), mar = rep(0, 4)) for(f in pi^(0:3)) contour(cos(r^2)*exp(-r/f), drawlabels = FALSE, axes = FALSE, frame = TRUE) rx <- range(x <- 10*1:nrow(volcano)) ry <- range(y <- 10*1:ncol(volcano)) ry <- ry + c(-1, 1) * (diff(rx) - diff(ry))/2 tcol <- terrain.colors(12) par(opar); opar <- par(pty = "s", bg = "lightcyan") plot(x = 0, y = 0, type = "n", xlim = rx, ylim = ry, xlab = "", ylab = "") u <- par("usr") rect(u[1], u[3], u[2], u[4], col = tcol[8], border = "red") contour(x, y, volcano, col = tcol[2], lty = "solid", add = TRUE, vfont = c("sans serif", "plain")) title("A Topographic Map of Maunga Whau", font = 4) abline(h = 200*0:4, v = 200*0:4, col = "lightgray", lty = 2, lwd = 0.1) ## contourLines produces the same contour lines as contour line.list <- contourLines(x, y, volcano) plot(x = 0, y = 0, type = "n", xlim = rx, ylim = ry, xlab = "", ylab = "") u <- par("usr") rect(u[1], u[3], u[2], u[4], col = tcol[8], border = "red") contour(x, y, volcano, col = tcol[2], lty = "solid", add = TRUE, vfont = c("sans serif", "plain")) templines <- function(clines) { lines(clines[[2]], clines[[3]]) } invisible(lapply(line.list, templines)) par(opar)

Documentation reproduced from R 3.0.2. License: GPL-2.