axis {graphics}R Documentation

Add an Axis to a Plot


Adds an axis to the current plot, allowing the specification of the side, position, labels, and other options.


axis(side, at = NULL, labels = TRUE, tick = TRUE, line = NA,
     pos = NA, outer = FALSE, font = NA,
     lty = "solid", lwd = 1, col = NULL, hadj = NA, padj = NA,


side an integer specifying which side of the plot the axis is to be drawn on. The axis is placed as follows: 1=below, 2=left, 3=above and 4=right.
at the points at which tick-marks are to be drawn. Non-finite (infinite, NaN or NA) values are omitted. By default, when NULL, tickmark locations are computed, see Details below.
labels this can either be a logical value specifying whether (numerical) annotations are to be made at the tickmarks, or a character or expression vector of labels to be placed at the tickpoints. (Other objects are coerced by as.graphicsAnnot.) If this is not logical, at should also be supplied and of the same length. If labels is of length zero after coercion, it has the same effect as supplying TRUE.
tick a logical value specifying whether tickmarks and an axis line should be drawn
line the number of lines into the margin which the axis will be drawn. If not NA this overrides the value of the graphical parameter mgp[3]. The relative placing of tickmarks and tick labels is unchanged.
pos the coordinate at which the axis line is to be drawn: if not NA this overrides the values of both line and mgp[3].
outer a logical value indicating whether the axis should be drawn in the outer plot margin, rather than the standard plot margin.
font font for text. Defaults to par("font").
lty, lwd line type, width for the axis line and the tick marks.
col color for the axis line and the tick marks. Here NULL means to use par("fg"), possibly specified inline.
hadj adjustment (see par("adj")) for all labels parallel (‘horizontal’) to the reading direction. If this is not a finite value, the default is used (centring for strings parallel to the axis, justification of the end nearest the axis otherwise).
padj adjustment for each tick label perpendicular to the reading direction. For labels parallel to the axes, padj=0 means right or top alignment, and padj=1 means left or bottom alignment. This can be a vector given a value for each string, and will be recycled as necessary.
If padj is not a finite value (the default), the value of par("las") determines the adjustment. For strings plotted perpendicular to the axis the default is to centre the string.
... other graphical parameters may also be passed as arguments to this function, particularly, cex.axis, col.axis and font.axis for axis annotation, mgp and xaxp or yaxp for positioning, tck or tcl for tick mark length and direction, las for vertical/horizontal label orientation, or fg instead of col, see par on these.
Parameters xaxt (sides 1 and 3) and yaxt (sides 2 and 4) control if the axis is plotted at all.
Note that xpd is not accepted as clipping is always to the device region, and that lab will partial match to argument labels unless the latter is also supplied. (Since the default axes has already been set up by plot.window, lab will not be acted on by axis.)


The axis line is drawn from the lowest to the highest value of at, but will be clipped at the plot region. Only ticks which are drawn from points within the plot region (up to a tolerance for rounding error) are plotted, but the ticks and their labels may well extend outside the plot region.

When at = NULL, pretty tick mark locations are computed internally (the same way axTicks(side) would) from par("xaxp") or "yaxp" and par("xlog") (or "ylog"). Note that these locations may change if an on-screen plot is resized (for example, if the plot argument asp (see plot.window) is set.)

If labels is not specified, the numeric values supplied or calculated for at are converted to character strings as if they were a numeric vector printed by print.default(digits=7).

The code tries hard not to draw overlapping tick labels, and so will omit labels where they would abut or overlap previously drawn labels. This can result in, for example, every other tick being labelled. (The ticks are drawn left to right or bottom to top, and space at least the size of an ‘m’ is left between labels.)

Several of the graphics parameters affect the way axes are drawn. The vertical (for sides 1 and 3) positions of the axis and the tick labels are controlled by mgp, the size and direction of the ticks is controlled by tck and tcl and the appearance of the tick labels by cex.axis, col.axis and font.axis with orientation controlled by las (but not srt, unlike S which uses srt if at is supplied and las if it is not). Note that adj is not supported. See par for details.


The numeric locations on the axis scale at which tick marks were drawn when the plot was first drawn (see Details).
This function is usually invoked for its side effect, which is to add an axis to an already existing plot.


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

See Also

Axis for a generic interface.

axTicks returns the axis tick locations corresponding to at=NULL; pretty is more flexible for computing pretty tick coordinates and does not depend on (nor adapt to) the coordinate system in use.

Several graphics parameters affecting the appearance are documented in par.


plot(1:4, rnorm(4), axes = FALSE)
axis(1, 1:4, LETTERS[1:4])
box() #- to make it look "as usual"

plot(1:7, rnorm(7), main = "axis() examples",
     type = "s", xaxt = "n", frame = FALSE, col = "red")
axis(1, 1:7, LETTERS[1:7], col.axis = "blue")
# unusual options:
axis(4, col = "violet", col.axis="dark violet", lwd = 2)
axis(3, col = "gold", lty = 2, lwd = 0.5)

# one way to have a custom x axis
plot(1:10, xaxt = "n")
axis(1, xaxp=c(2, 9, 7))

[Package graphics version 2.5.0 Index]