coord_map.Rd

% Generated by roxygen2 (4.1.1): do not edit by hand
% Please edit documentation in R/coord-map.r, R/coord-quickmap.R
\name{coord_map}
\alias{coord_map}
\alias{coord_quickmap}
\title{Map projections.}
\usage{
coord_map(projection = "mercator", ..., orientation = NULL, xlim = NULL,
  ylim = NULL)

coord_quickmap(xlim = NULL, ylim = NULL)
}
\arguments{
\item{projection}{projection to use, see
\code{\link[mapproj]{mapproject}} for list}

\item{...}{other arguments passed on to
\code{\link[mapproj]{mapproject}}}

\item{orientation}{projection orientation, which defaults to
\code{c(90, 0, mean(range(x)))}.  This is not optimal for many
projections, so you will have to supply your own. See
\code{\link[mapproj]{mapproject}} for more information.}

\item{xlim}{manually specific x limits (in degrees of longitude)}

\item{ylim}{manually specific y limits (in degrees of latitude)}
}
\description{
The representation of a portion of the earth, which 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 correctness in the projection.
This coordinate system provides the full range of map projections available
in the mapproj package.
}
\examples{
if (require("maps")) {
nz <- map_data("nz")
# Prepare a map of NZ
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()

# Other projections
nzmap + coord_map("cylindrical")
nzmap + coord_map("azequalarea",orientation=c(-36.92,174.6,0))

states <- map_data("state")
usamap <- ggplot(states, aes(long, lat, group = group)) +
  geom_polygon(fill = "white", colour = "black")

# Use cartesian coordinates
usamap
# With mercator projection
usamap + coord_map()
usamap + coord_quickmap()
# See ?mapproject for coordinate systems and their parameters
usamap + coord_map("gilbert")
usamap + coord_map("lagrange")

# For most projections, you'll need to set the orientation yourself
# as the automatic selection done by mapproject is not available to
# ggplot
usamap + coord_map("orthographic")
usamap + coord_map("stereographic")
usamap + coord_map("conic", lat0 = 30)
usamap + coord_map("bonne", lat0 = 50)

# World map, using geom_path instead of geom_polygon
world <- map_data("world")
worldmap <- ggplot(world, aes(x=long, y=lat, group=group)) +
  geom_path() +
  scale_y_continuous(breaks = (-2:2) * 30) +
  scale_x_continuous(breaks = (-4:4) * 45)

# Orthographic projection with default orientation (looking down at North pole)
worldmap + coord_map("ortho")
# Looking up up at South Pole
worldmap + coord_map("ortho", orientation = c(-90, 0, 0))
# Centered on New York (currently has issues with closing polygons)
worldmap + coord_map("ortho", orientation = c(41, -74, 0))
}
}