- asp:
If asp is a finite positive value then the window is
set up so that one data unit in the x direction is equal in length to
asp \(\times\) one data unit in the y direction.
Note that in this case, par("usr") is no longer
determined by, e.g., par("xaxs"), but rather by asp and
the device's aspect ratio. (See what happens if you interactively
resize the plot device after running the example below!)
The special case asp == 1 produces plots where distances
between points are represented accurately on screen. Values with
asp > 1 can be used to produce more accurate maps when using
latitude and longitude.
Note that the coordinate ranges will be extended by 4% if the
appropriate graphical parameter xaxs or yaxs has value
"r" (which is the default).
To reverse an axis, use xlim or ylim of the form
c(hi, lo).
The function attempts to produce a plausible set of scales if one or
both of xlim and ylim is of length one or the two values
given are identical, but it is better to avoid that case.
Usually, one should rather use the higher-level functions such as
plot, hist, image, …,
instead and refer to their help pages for explanation of the
arguments.
A side-effect of the call is to set up the usr, xaxp and
yaxp graphical parameters. (It is for the latter two that
lab is used.)