Set up World Coordinates for Graphics Window
Description
This function sets up the world coordinate system for a graphics
window. It is called by higher level functions such as
plot.default
(after plot.new
).
Usage
1 
Arguments
xlim, ylim 
numeric vectors of length 2, giving the x and y coordinates ranges. 
log 
character; indicating which axes should be in log scale. 
asp 
numeric, giving the aspect ratio y/x, see ‘Details’. 
... 
further graphical parameters as in 
Details
 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 toasp
* 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 byasp
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 withasp > 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 higherlevel functions such as
plot
, hist
, image
, ...,
instead and refer to their help pages for explanation of the
arguments.
A sideeffect of the call is to set up the usr
, xaxp
and
yaxp
graphical parameters. (It is for the latter two that
lab
is used.)
See Also
xy.coords
,
plot.xy
,
plot.default
.
par
for the graphical parameters mentioned.
Examples
1 2 3 4 5 6 7 8  ## An example for the use of 'asp' :
require(stats) # normally loaded
loc < cmdscale(eurodist)
rx < range(x < loc[,1])
ry < range(y < loc[,2])
plot(x, y, type = "n", asp = 1, xlab = "", ylab = "")
abline(h = pretty(rx, 10), v = pretty(ry, 10), col = "lightgray")
text(x, y, labels(eurodist), cex = 0.8)
