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\name{plot.window}
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\alias{plot.window}
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\alias{asp}
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\concept{aspect ratio}
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\title{Set up World Coordinates for Graphics Window}
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\description{
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This function sets up the world coordinate system for a graphics
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window. It is called by higher level functions such as
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\code{\link{plot.default}} (\emph{after} \code{\link{plot.new}}).
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}
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\usage{
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plot.window(xlim, ylim, log = "", asp = NA, \dots)
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}
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\arguments{
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\item{xlim, ylim}{numeric vectors of length 2, giving the x and y
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coordinates ranges.}
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\item{log}{character; indicating which axes should be in log scale.}
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\item{asp}{numeric, giving the \bold{asp}ect ratio y/x.}
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\item{\dots}{further graphical parameters as in \code{\link{par}}.
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The relevant ones are \code{xaxs}, \code{yaxs} and \code{lab}.
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}
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}
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\details{
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Note that if \code{asp} is a finite positive value then the window is
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set up so that one data unit in the x direction is equal in length to
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\code{asp} \eqn{\times}{*} one data unit in the y direction.
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The special case \code{asp == 1} produces plots where distances
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between points are represented accurately on screen. Values with
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\code{asp > 1} can be used to produce more accurate maps when using
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latitude and longitude.
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To reverse an axis, use \code{xlim} or \code{ylim} of the form
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\code{c(hi, lo)}.
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The function attempts to produce a plausible set of scales if one or
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both of \code{xlim} and \code{ylim} is of length one or the two values
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given are identical, but it is better to avoid that case.
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Usually, one should rather use the higher level functions such as
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\code{\link{plot}}, \code{\link{hist}}, \code{\link{image}}, \dots,
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instead and refer to their help pages for explanation of the
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arguments.
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A side-effect of the call is to set up the \code{usr}, \code{xaxp} and
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\code{yaxp} graphical parameters. (It is for the latter two that
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\code{lab} is used.)
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}
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\seealso{
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\code{\link{xy.coords}},
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\code{\link{plot.xy}},
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\code{\link{plot.default}}.
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}
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\examples{
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##--- An example for the use of 'asp' :
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require(stats) # normally loaded
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loc <- cmdscale(eurodist)
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rx <- range(x <- loc[,1])
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ry <- range(y <- -loc[,2])
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plot(x, y, type="n", asp=1, xlab="", ylab="")
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abline(h = pretty(rx, 10), v = pretty(ry, 10), col = "lightgray")
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text(x, y, labels(eurodist), cex=0.8)
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}
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\keyword{aplot}
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