coord_quickmap.Rd

% Generated by roxygen2 (4.1.0): do not edit by hand
% Please edit documentation in R/coord-quickmap.R
\name{coord_quickmap}
\alias{coord_quickmap}
\title{Cartesian coordinates with an aspect ratio approximating Mercator projection.}
\usage{
coord_quickmap(xlim = NULL, ylim = NULL)
}
\arguments{
\item{xlim}{limits for the x axis}

\item{ylim}{limits for the y axis}
}
\description{
The represenation of a portion of the earth, wich is approximately spherical,
onto a flat 2D plane requires a projection. This is what
\code{\link{coord_map}} does. These projections account for the fact that the
actual length (in km) of one degree of longitude varies between the equator
and the pole. Near the equator, the ratio between the lengths of one degree
of latitude and one degree of longitude is approximately 1. Near the pole, it
is tends towards infinity because the length of one degree of longitude tends
towards 0. For regions that span only a few degrees and are not too close to
the poles, setting the aspect ratio of the plot to the appropriate lat/lon
ratio approximates the usual mercator projection. This is what
\code{coord_quickmap} does. With \code{\link{coord_map}} all elements of the
graphic have to be projected which is not the case here. So
\code{\link{coord_quickmap}} has the advantage of being much faster, in
particular for complex plots such as those using with
\code{\link{geom_tile}}, at the expense of correctedness in the projection.
}
\examples{
# ensures that the ranges of axes are equal to the specified ratio by
# adjusting the plot aspect ratio

if (require("maps")) {
# Create a lat-long dataframe from the maps package
nz <- map_data("nz")
# Prepare a plot of the map
nzmap <- ggplot(nz, aes(x = long, y = lat, group = group)) +
  geom_polygon(fill = "white", colour = "black")

# Plot it in cartesian coordinates
nzmap
# With correct mercator projection
nzmap + coord_map()
# With the aspect ratio approximation
nzmap + coord_quickmap()
}

# Resize the plot to see that the specified aspect ratio is maintained
}