mapproject  R Documentation 
Converts latitude and longitude into projected coordinates.
mapproject(x, y, projection="", parameters=NULL, orientation=NULL)
x,y 
two vectors giving longitude and latitude coordinates
of points on the earth's surface to be projected.
A list containing components named 
projection 
optional character string that names a map projection to
use. If the string is 
parameters 
optional numeric vector of parameters for use with the

orientation 
An optional vector 
Each standard projection is displayed with the Prime
Meridian (longitude 0) being a straight vertical line, along which North
is up.
The orientation of nonstandard projections is specified by
the three parameters=c(lat,lon,rot)
.
Imagine a transparent gridded sphere around the globe.
First turn the overlay about the North Pole
so that the Prime Meridian (longitude 0)
of the overlay coincides with meridian lon
on the globe.
Then tilt the North Pole of the
overlay along its Prime Meridian to latitude lat
on the globe.
Finally again turn the
overlay about its "North Pole" so
that its Prime Meridian coincides with the previous position
of (the overlay) meridian rot
.
Project the desired map in
the standard form appropriate to the overlay, but presenting
information from the underlying globe.
In the descriptions that follow each projection is shown as a function call; if it requires parameters, these are shown as arguments to the function. The descriptions are grouped into families.
Equatorial projections centered on the Prime Meridian (longitude 0). Parallels are straight horizontal lines.
equally spaced straight meridians, conformal, straight compass courses
equally spaced parallels, equalarea, same
as bonne(0)
equally spaced straight meridians,
equalarea, true scale on lat0
central projection on tangent cylinder
equally spaced parallels, equally
spaced straight meridians, true scale on lat0
parallels
spaced stereographically on prime meridian, equally spaced straight
meridians, true scale on lat0
(homalographic) equalarea, hemisphere is a circle
sphere conformally mapped on hemisphere and viewed orthographically
Azimuthal projections centered on the North Pole. Parallels are concentric circles. Meridians are equally spaced radial lines.
equally spaced parallels, true distances from pole
equalarea
central projection on tangent plane, straight great circles
viewed along earth's axis dist
earth radii from center of earth
viewed from infinity
conformal, projected from opposite pole
radius = tan(2 * colatitude)
used in xray crystallography
stereographic seen through medium with refractive
index n
radius = log(colatitude/r)
map from viewing
pedestal of radius r
degrees
Polar conic projections symmetric about the Prime Meridian. Parallels are segments of concentric circles. Except in the Bonne projection, meridians are equally spaced radial lines orthogonal to the parallels.
central projection on cone tangent at lat0
equally spaced parallels, true scale on lat0
and lat1
conformal, true scale on lat0
and lat1
equalarea, true scale on lat0
and lat1
equally spaced parallels, equalarea, parallel lat0
developed from tangent cone
Projections with bilateral symmetry about the Prime Meridian and the equator.
parallels developed from tangent cones, equally spaced along Prime Meridian
equalarea
projection of globe onto 2to1 ellipse, based on azequalarea
conformal, maps whole sphere into a circle
points plotted at true azimuth from two centers on the
equator at longitudes +lon0
and lon0
, great circles are
straight lines (a stretched gnomonic projection)
points are
plotted at true distance from two centers on the equator at longitudes
+lon0
and lon0
hemisphere is circle, circular arc meridians equally spaced on equator, circular arc parallels equally spaced on 0 and 90degree meridians
sphere is circle, meridians as
in globular
, circular arc parallels resemble mercator
conformal with no singularities, shaped like polyconic
Doubly periodic conformal projections.
W and E hemispheres are square
world is square with Poles at diagonally opposite corners
map on tetrahedron with edge tangent to Prime Meridian at S Pole, unfolded into equilateral triangle
world is hexagon centered on N Pole, N and S hemispheres are equilateral triangles
Miscellaneous projections.
oblique
perspective from above the North Pole, dist
earth radii from center of
earth, looking along the Date Line angle
degrees off vertical
equally spaced parallels, straight meridians
equally spaced along parallels, true scale at lat0
and lat1
on Prime
Meridian
conformal, polar cap above latitude lat
maps to convex lune with given angle
at 90E and 90W
Retroazimuthal projections. At every point the angle between vertical
and a straight line to "Mecca", latitude lat0
on the prime meridian,
is the true bearing of Mecca.
equally spaced vertical meridians
distances to Mecca are true
Maps based on the spheroid. Of geodetic quality, these projections do not make sense for tilted orientations.
Mercator on the spheroid.
Albers on the spheroid.
list with components
named x
and y
, containing the projected coordinates.
NA
s project to NA
s.
Points deemed unprojectable (such as north of 80 degrees
latitude in the Mercator projection) are returned as NA
.
Because of the ambiguity of the first two arguments, the other
arguments must be given by name.
Each time mapproject
is called, it leaves on frame 0 the
dataset .Last.projection
, which is a list with components projection
,
parameters
, and orientation
giving the arguments from the
call to mapproject
or as constructed (for orientation
).
Subsequent calls to mapproject
will get missing information
from .Last.projection
.
Since map
uses mapproject
to do its projections, calls to
mapproject
after a call to map
need not supply any arguments
other than the data.
Richard A. Becker, and Allan R. Wilks, "Maps in S", AT&T Bell Laboratories Statistics Research Report, 1991. https://web.archive.org/web/20070824013345/http://www.research.att.com/areas/stat/doc/93.2.ps
M. D. McIlroy, Documentation from the Tenth Edition UNIX Manual, Volume 1, Saunders College Publishing, 1990.
library(maps) # Bonne equalarea projection with state abbreviations map("state",proj='bonne', param=45) data(state) text(mapproject(state.center), state.abb) # this does not work because the default orientations are different: map("state",proj='bonne', param=45) text(mapproject(state.center,proj='bonne',param=45),state.abb) map("state",proj="albers",par=c(30,40)) map("state",par=c(20,50)) # another Albers projection map("world",proj="gnomonic",orient=c(0,100,0)) # example of orient # see map.grid for more examples # tests of projections added RSB 091101 projlist < c("aitoff", "albers", "azequalarea", "azequidist", "bicentric", "bonne", "conic", "cylequalarea", "cylindrical", "eisenlohr", "elliptic", "fisheye", "gall", "gilbert", "guyou", "harrison", "hex", "homing", "lagrange", "lambert", "laue", "lune", "mercator", "mollweide", "newyorker", "orthographic", "perspective", "polyconic", "rectangular", "simpleconic", "sinusoidal", "tetra", "trapezoidal") x < seq(100, 0, 10) y < seq(45, 45, 10) xy < expand.grid(x=x, y=y) pf < c(0, 2, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 0, 2, 0, 1, 0, 2, 0, 2, 0, 0, 1, 0, 1, 0, 1, 2, 0, 0, 2) res < vector(mode="list", length=length(projlist)) for (i in seq(along=projlist)) { if (pf[i] == 0) res[[i]] < mapproject(xy$x, xy$y, projlist[i]) else if (pf[i] == 1) res[[i]] < mapproject(xy$x, xy$y, projlist[i], 0) else res[[i]] < mapproject(xy$x, xy$y, projlist[i], c(0,0)) } names(res) < projlist lapply(res, function(p) rbind(p$x, p$y))
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