plot function

Plot a Raster* object

Plot (that is, make a map of) the values of a Raster* object, or make a scatterplot of their values.

Points, lines, and polygons can be drawn on top of a map using plot(..., add=TRUE), or with functions like points, lines, polygons

See the rasterVis package for more advanced (trellis/lattice) plotting of Raster* objects. methods

## S4 method for signature 'Raster,ANY'
plot(x, y, maxpixels=500000, col, alpha=NULL,
   colNA=NA, add=FALSE, ext=NULL, useRaster=TRUE, interpolate=FALSE, 
   addfun=NULL, nc, nr, maxnl=16, main, npretty=0, ...)
   

## S4 method for signature 'Raster,Raster'
plot(x, y, maxpixels=100000, cex, xlab, ylab, nc, nr, 
    maxnl=16, main, add=FALSE, gridded=FALSE, ncol=25, nrow=25, ...)

Arguments

• x: Raster* object
• y: If x is a RasterStack or RasterBrick: integer, character (layer name(s)), or missing to select which layer(s) to plot. If missing, all RasterLayers in the RasterStack will be plotted (up to a maximum of 16). Or another Raster* object of the same extent and resolution, to produce a scatter plot of the cell values.
• maxpixels: integer > 0. Maximum number of cells to use for the plot. If maxpixels < ncell(x), sampleRegular is used before plotting. If gridded=TRUE maxpixels may be ignored to get a larger sample
• col: A color palette, i.e. a vector of n contiguous colors generated by functions like rainbow , heat.colors , topo.colors , bpy.colors or one or your own making, perhaps using colorRampPalette. If none is provided, rev(terrain.colors(255)) is used unless x has a 'color table'
• alpha: Number between 0 and 1 to set transparency. 0 is entirely transparent, 1 is not transparent (NULL is equivalent to 1)
• colNA: The color to use for the background (default is transparent)
• add: Logical. Add to current plot?
• ext: An extent object to zoom in a region (see also zoom and crop(x, drawExtent())
• useRaster: If TRUE, the rasterImage function is used for plotting. Otherwise the image function is used. This can be useful if rasterImage does not work well on your system (see note)
• interpolate: Logical. Should the image be interpolated (smoothed)? Only used when useRaster = TRUE
• addfun: Function to add additional items such as points or polygons to the plot (map). Typically containing statements like "points(xy); plot(polygons, add=TRUE)". This is particularly useful to add something to each map when plotting a multi-layer Raster* object.
• npretty: integer. Number of decimals for pretty lables on the axes
• ...: Graphical parameters. Any argument that can be passed to image.plot and to base plot, such as axes=FALSE, main='title', ylab='latitude'
• xlab: Optional. x-axis label)
• ylab: Optional. y-axis label)
• nc: Optional. The number of columns to divide the plotting device in (when plotting multiple layers in a RasterLayer or RasterBrick object)
• nr: Optional. The number of rows to divide the plotting device in (when plotting multiple layers in a RasterLayer or RasterBrick object)
• maxnl: integer. Maximum number of layers to plot (for a multi-layer object)
• main: character. Main plot title
• cex: Symbol size for scatter plots
• gridded: logical. If TRUE the scatterplot is gridded (counts by cells)
• ncol: integer. Number of columns for gridding
• nrow: integer. Number of rows for gridding

Details

Most of the code for the plot function for a single Raster* object was taken from image.plot (fields package).

Raster objects with a color-table (e.g. a graphics file) are plotted according to that color table.

Note

raster uses rasterImage from the graphics package. For unknown reasons this does not work on Windows Server and on a few versions of Windows XP. On that system you may need to use argument useRaster=FALSE to get a plot.

See Also

The rasterVis package has lattice based methods for plotting Raster* objects (like spplot)

red-green-blue plots (e.g. false color composites) can be made with plotRGB

barplot, hist, text, persp, contour, pairs

Examples

# RasterLayer
r <- raster(nrows=10, ncols=10)
r <- setValues(r, 1:ncell(r))
plot(r)

e <- extent(r)
plot(e, add=TRUE, col='red', lwd=4)
e <- e / 2
plot(e, add=TRUE, col='red')

# Scatterplot of 2 RasterLayers
r2 <- sqrt(r)
plot(r, r2)
plot(r, r2, gridded=TRUE)

# Multi-layer object (RasterStack / Brick)
s <- stack(r, r2, r/r)
plot(s, 2)
plot(s)

# two objects, different range, one scale:
values(r) <- runif(ncell(r))
r2 <- r/2
brks <- seq(0, 1, by=0.1) 
nb <- length(brks)-1 
cols <- rev(terrain.colors(nb))
par(mfrow=c(1,2))
plot(r, breaks=brks, col=cols, lab.breaks=brks, zlim=c(0,1), main='first') 
plot(r2, breaks=brks, col=cols, lab.breaks=brks, zlim=c(0,1), main='second') 

# breaks and labels
x <- raster(nc=10, nr=10)
values(x) <- runif(ncell(x))
brk <- c(0, 0.25, 0.75, 1)
arg <- list(at=c(0.12,0.5,0.87), labels=c("Low","Med.","High"))
plot(x, col=terrain.colors(3), breaks=brk)
plot(x, col=terrain.colors(3), breaks=brk, axis.args=arg)
par(mfrow=c(1,1))

# color ramp
plot(x, col=colorRampPalette(c("red", "white", "blue"))(255))

# adding random points to the map
xy <- cbind(-180 + runif(10) * 360, -90 + runif(10) * 180)
points(xy, pch=3, cex=5)

# for SpatialPolygons do
# plot(pols, add=TRUE)

# adding the same points to each map of each layer of a RasterStack
fun <- function() {
        points(xy, cex=2)
        points(xy, pch=3, col='red')
}
plot(s, addfun=fun)