Usage
mapPlot(longitude, latitude, longitudelim, latitudelim,
grid=TRUE, bg, fill, border=NULL, col=NA, type='l', axes=TRUE, drawBox=TRUE,
showHemi=TRUE, polarCircle=0,
lonlabel=NULL, latlabel=NULL, sides=NULL,
projection="+proj=moll", tissot=FALSE, trim=TRUE,
debug=getOption("oceDebug"), ...)Arguments
longitude
either a vector of longitudes of points to be plotted, or
something (an oce object, a list, or a data frame) from which both
longitude and latitude may be inferred (in which case the latitude
argument is ignored). If
latitude
latitudes of points to be plotted (ignored if the first
argument contains both latitude and longitude).
longitudelim
optional limit of longitudes to plot
latitudelim
optional limit of latitudes to plot
grid
either a number (or pair of numbers) indicating the spacing of
longitude and latitude lines, in degrees, or a logical value (or pair of
values) indicating whether to draw an auto-scaled grid, or whether to skip
the grid drawing. In the case o
bg
background colour for plot (ignored at present).
fill
included only for compatibility with the previous version of
mapPlot; will be removed in next version.
border
colour of coastlines and international borders. The default,
NULL, means to use par("fg"); see
polygon. col
colour with which to fill coastline elements. The default,
NA, is not to fill; see polygon. type
value to indicate type of plot, as with
par("plot"). axes
logical value indicating whether to draw longitude and latitude
values in the lower and left margin, respectively. This may not work well
for some projections or scales.
drawBox
logical value indicating whether to draw a box around the plot.
This is helpful for many projections at sub-global scale.
showHemi
logical value indicating whether to show the hemisphere in
axis tick labels.
polarCircle
a number indicating the number of degrees of latitude
extending from the poles, within which zones are not drawn.
lonlabel,latlabel,sides
optional vectors of longitude and latitude
to label on the indicated sides of plot, passed to
plot.coastline. Using these arguments permits reasonably
simple customization. If they are projection
optional indication of projection, a character string that
in the format used by the rgdal package (and in much of computer
cartography). For example, projection="+proj=merc" specifies a
Mercator projection. See
trim
a logical value indicating whether to trim islands or lakes
containing only points that are off-scale of the current plot box. This
solves the problem of Antarctica overfilling the entire domain, for an
Arctic-centred stereographic projection
tissot
logical indicating whether to use mapTissot to
plot Tissot indicatrices, i.e. ellipses at grid intersection points, which
indicate map distortion. debug
a flag that turns on debugging. Set to 1 to get a moderate
amount of debugging information, or to 2 to get more.
...
optional arguments passed to some plotting functions. This can
be useful in many ways, e.g. Example 5 shows how to use xlim etc to
reproduce a scale exactly between two plots.
Available Projections
Map projections are provided by the
rgdal package, but not all projections in that package are
available. The available list is given in the table
below. The cartographic community has set up a naming scheme in a coded
scheme, e.g. projection="+proj=aea" selects the Albers equal area
projection. The allowed projections include those PROJ.4 projections provided by
rgdal that have inverses, minus a few that cause problems:
alsk overdraws coastlineWorld, and is a niche projection for Alaska;
calcofi is not a real projection, but rather a coordinate system;
gs48 overdraws coastlineWorld, and is a niche projection for the USA;
gs50 overdraws coastlineWorld, and is a niche projection for the USA;
gstmerc overdraws coastlineWorld;
isea causes segmentation faults on OSX systems;
krovak overdraws coastlineWorld, and is a niche projection for the Czech Republic;
labrd returns NaN for most of the world, and is a niche projection for Madagascar;
lee_os overdraws coastlineWorld;
and
nzmg overdraws coastlineWorld.
The information in the table is reformatted from the output of the unix
command proj -lP, where proj is provided by version 4.9.0 of
the PROJ.4 system. Most of the arguments listed have default values. In
addition, most projections can handle arguments lon_0 and
lat_0, for shifting the reference point, although in some cases
shifting the longitude can yield poor filling of coastlines.
Further details of the projections and the controlling arguments are
provided at several websites, because PROJ.4 has been incorporated into
rgdal and other R packages, plus many other software systems; a good
starting point for learning is [6].
See Examples for suggested projections for some common
applications, and [8] for a gallery indicating how to use every projection.
lll{
Projection Code Arguments
Albers equal area aea lat_1, lat_2
Azimuthal equidistant aeqd lat_0, guam
Aitoff aitoff -
Mod. stererographics of Alaska alsk -
Bipolar conic of western hemisphere bipc -
Bonne Werner bonne lat_1
Cassini cass -
Central cylindrical cc -
Equal area cylindrical cea lat_ts
Collignon collg -
Craster parabolic Putnins P4 crast -
Eckert I eck1 -
Eckert II eck2 -
Eckert III eck3 -
Eckert IV eck4 -
Eckert V eck5 -
Eckert VI eck6 -
Equidistant cylindrical plate (Caree) eqc lat_ts, lat_0
Equidistant conic eqdc lat_1, lat_2
Euler euler lat_1, lat_2
Extended transverse Mercator etmerc lat_ts, lat_0
Fahey fahey -
Foucaut fouc -
Foucaut sinusoidal fouc_s -
Gall stereographic gall -
Geostationary satellite view geos h
General sinusoidal series gn_sinu m, n
Gnomonic gnom -
Goode homolosine goode -
Hatano asymmetrical equal area hatano -
HEALPix healpix -
rHEALPix rhealpix north_square, south_square
Interrupted Goode homolosine igh -
Int'l map of the world polyconic imw_p lat_1, lat_2, lon_1
Kavraisky V kav5 -
Kavraisky VII kav7 -
Lambert azimuthal equal area laea -
Lat/long lonlat -
Lat/long latlon -
Lambert conformal conic lcc lat_1, lat_2, lat_0
Lambert conformal conic alternative lcca lat_0
Lambert equal area conic leac lat_1, south
Loximuthal loxim
Space oblique for Landsat lsat lsat, path
McBryde-Thomas flat-polar sine, no. 1 mbt_s
McBryde-Thomas flat-polar sine, no. 2 mbt_fps
McBryde-Thomas flat-polar parabolic mbtfpp
McBryde-Thomas flat-polar quartic mbtfpq
McBryde-Thomas flat-polar sinusoidal mbtfps
Mercator merc lat_ts
Miller oblated stereographic mil_os
Miller cylindrical mill
Mollweide moll
Murdoch I murd1 lat_1, lat_2
Murdoch II murd2 lat_1, lat_2
murdoch III murd3 lat_1, lat_2
Natural earth natearth
Nell nell
Nell-Hammer nell_h
Near-sided perspective nsper h
New Zealand map grid nzmg
General oblique transformation ob_tran o_proj, o_lat_p, o_lon_p, o_alpha, o_lon_c
o_lat_c, o_lon_1, o_lat_1, o_lon_2, o_lat_2
Oblique cylindrical equal area ocea lat_1, lat_2, lon_1, lon_2
Oblated equal area oea n, m, theta
Oblique Mercator omerc alpha, gamma, no_off, lonc, lon_1,
lat_1, lon_2, lat_2
Orthographic ortho -
Perspective conic pconic lat_1, lat_2
Polyconic American poly -
Putnins P1 putp1 -
Putnins P2 putp2 -
Putnins P3 putp3 -
Putnins P3' putp3p -
Putnins P4' putp4p -
Putnins P5 putp5 -
Putnins P5' putp5p -
Putnins P6 putp6 -
Putnins P6' putp6p -
Quartic authalic qua_aut -
Quadrilateralized spherical cube qsc -
Robinson robin -
Roussilhe stereographic rouss -
Sinusoidal aka Sanson-Flamsteed sinu -
Swiss. oblique Mercator somerc -
Stereographic stere lat_ts
Oblique stereographic alternative sterea -
Gauss-schreiber transverse Mercator gstmerc lat_0, lon_0, k_0
Transverse cylindrical equal area tcea -
Tissot tissot lat_1, lat_2
Transverse Mercator tmerc -
Two point equidistant tpeqd lat_1, lon_1, lat_2, lon_2
Tilted perspective tpers tilt, azi, h
Universal polar stereographic ups south
Urmaev flat-polar sinusoidal urmfps n
Universal transverse Mercator utm zone, south
van der Grinten I vandg -
Vitkovsky I vitk1 lat_1, lat_2
Wagner I Kavraisky VI wag1 -
Wagner II wag2 -
Wagner III wag3 lat_ts
Wagner IV wag4 -
Wagner V wag5 -
Wagner VI wag6 -
Werenskiold I weren -
Winkel I wink1 lat_ts
Winkel Tripel wintri lat_ts
}
Available ellipse formulations
In the PROJ.4 system of specifying
projections, the following ellipse models are available: MERIT,
SGS85, GRS80, IAU76, airy, APL4.9,
NWL9D, mod_airy, andrae, aust_SA, GRS67,
bessel, bess_nam, clrk66, clrk80,
clrk80ign, CPM, delmbr, engelis,
evrst30, evrst48, evrst56, evrst69,
evrstSS, fschr60, fschr60m, fschr68,
helmert, hough, intl, krass, kaula,
lerch, mprts, new_intl, plessis, SEasia,
walbeck, WGS60, WGS66, WGS72, WGS84, and
sphere (the default). For example, use projection="+proj=aea
+ellps=WGS84" for an Albers Equal Area projection using the most
recent of the World Geodetic System model. It is unlikely that changing the
ellipse will have a visible effect on plotted material at the plot scale
appropriate to most oceanographic applications.Available datum formulations
In the PROJ.4 system of specifying
projections, the following datum formulations are available: WGS84,
GGRS87, Greek_Geodetic_Reference_System_1987, NAD83,
North_American_Datum_1983, NAD27,
North_American_Datum_1927, potsdam, Potsdam,
carthage, Carthage, hermannskogel,
Hermannskogel, ire65, Ireland, nzgd49,
New, OSGB36, and Airy. It is unlikely that changing
the datum will have a visible effect on plotted material at the plot scale
appropriate to most oceanographic applications.Choosing a projection
The use of the PROJ.4 scheme is greatly
encouraged. The best choice of projection depends on the application.
Readers may find projection="+proj=moll" useful for world-wide
plots, ortho for hemispheres viewed from the equator, stere
for polar views, lcc for wide meridional ranges in mid latitudes,
and merc in limited-area cases where angle preservation is
important.Issues
Map projection is a complicated matter that is addressed here
in a limited and pragmatic way. For example, mapPlot tries to draw
axes along a box containing the map, instead of trying to find spots along
the ``edge'' of the map at which to put longitude and latitude labels.
This design choice greatly simplifies the coding effort, freeing up time to
work on issues regarded as more pressing. Chief among those issues are (a)
the occurrence of horizontal lines in maps that have prime meridians
(b) inaccurate filling of land regions that (again) occur with shifted
meridians and (c) inaccurate filling of Antarctica in some projections.
Generally, issues are tackled first for commonly used projections, such as
those used in the examples.