R: Level (Contour) Plots

filled.contour {graphics} | R Documentation

## Level (Contour) Plots

### Description

This function produces a contour plot with the areas between the contours filled in solid color (Cleveland calls this a level plot). A key showing how the colors map to z values is shown to the right of the plot.

### Usage

    filled.contour(x = seq(0, 1, length.out = nrow(z)),
                   y = seq(0, 1, length.out = ncol(z)),
                   z,
                   xlim = range(x, finite=TRUE),
                   ylim = range(y, finite=TRUE),
                   zlim = range(z, finite=TRUE),
                   levels = pretty(zlim, nlevels), nlevels = 20,
                   color.palette = cm.colors,
                   col = color.palette(length(levels) - 1),
                   plot.title, plot.axes, key.title, key.axes,
                   asp = NA, xaxs = "i", yaxs = "i", las = 1,
                   axes = TRUE, frame.plot = axes, ...)

### 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.
`xlim` | x limits for the plot.
`ylim` | y limits for the plot.
`zlim` | z limits for the plot.
`levels` | a set of levels which are used to partition the range of `z`. Must be strictly increasing (and finite). Areas with `z` values between consecutive levels are painted with the same color.
`nlevels` | if `levels` is not specified, the range of `z`, values is divided into approximately this many levels.
`color.palette` | a color palette function to be used to assign colors in the plot.
`col` | an explicit set of colors to be used in the plot. This argument overrides any palette function specification.
`plot.title` | statements which add titles to the main plot.
`plot.axes` | statements which draw axes (and a `box`) on the main plot. This overrides the default axes.
`key.title` | statements which add titles for the plot key.
`key.axes` | statements which draw axes on the plot key. This overrides the default axis.
`asp` | the y/x aspect ratio, see `plot.window`.
`xaxs` | the x axis style. The default is to use internal labeling.
`yaxs` | the y axis style. The default is to use internal labeling.
`las` | the style of labeling to be used. The default is to use horizontal labeling.
`axes, frame.plot` | logicals indicating if axes and a box should be drawn, as in `plot.default`.
`...` | additional graphical parameters, currently only passed to `title()`.

### Note

This function currently uses the `layout` function and so is restricted to a full page display. As an alternative consider the `levelplot` and `contourplot` functions from the lattice package which work in multipanel displays.

The output produced by `filled.contour` is actually a combination of two plots; one is the filled contour and one is the legend. Two separate coordinate systems are set up for these two plots, but they are only used internally - once the function has returned these coordinate systems are lost. If you want to annotate the main contour plot, for example to add points, you can specify graphics commands in the `plot.axes` argument. An example is given below.

### Author(s)

Ross Ihaka.

### References

Cleveland, W. S. (1993) Visualizing Data. Summit, New Jersey: Hobart.

### See Also

`contour`, `image`, `palette`; `contourplot` from package lattice.

### Examples

    require(grDevices) # for colours
    filled.contour(volcano, color = terrain.colors, asp = 1)# simple

    x <- 10*1:nrow(volcano)
    y <- 10*1:ncol(volcano)
    filled.contour(x, y, volcano, color = terrain.colors,
        plot.title = title(main = "The Topography of Maunga Whau",
        xlab = "Meters North", ylab = "Meters West"),
        plot.axes = { axis(1, seq(100, 800, by = 100))
                      axis(2, seq(100, 600, by = 100)) },
        key.title = title(main="Height\n(meters)"),
        key.axes = axis(4, seq(90, 190, by = 10)))# maybe also asp=1
    mtext(paste("filled.contour(.) from", R.version.string),
          side = 1, line = 4, adj = 1, cex = .66)

    # Annotating a filled contour plot
    a <- expand.grid(1:20, 1:20)
    b <- matrix(a[,1] + a[,2], 20)
    filled.contour(x = 1:20, y = 1:20, z = b,
                   plot.axes={ axis(1); axis(2); points(10,10) })

    ## Persian Rug Art:
    x <- y <- seq(-4*pi, 4*pi, len = 27)
    r <- sqrt(outer(x^2, y^2, "+"))
    filled.contour(cos(r^2)*exp(-r/(2*pi)), axes = FALSE)
    ## rather, the key *should* be labeled:
    filled.contour(cos(r^2)*exp(-r/(2*pi)), frame.plot = FALSE,
                   plot.axes = {})

[Package graphics version 2.8.1 Index]