Plot coordinates as a map, using one of the subset of projections
provided by the sf package. The projection information specified
with the mapPlot() call is stored in a global variable that can be retrieved
by related functions, making it easy to add points, lines, text, images
or contours to an existing map.
The “Details” section, below, provides a list of
available projections. The "Using map projections" vignette
offers examples of several map plots, in addition to the single
example provided in the “Examples” section, below.
mapPlot(
longitude,
latitude,
longitudelim,
latitudelim,
grid = TRUE,
geographical = 0,
bg,
fill,
border = NULL,
col = NULL,
clip = TRUE,
type = "polygon",
axes = TRUE,
axisStyle = 1,
cex,
cex.axis = 1,
mgp = c(0, 0.5, 0),
drawBox = TRUE,
showHemi = TRUE,
polarCircle = 0,
lonlabels = TRUE,
latlabels = TRUE,
projection = "+proj=moll",
tissot = FALSE,
trim = TRUE,
debug = getOption("oceDebug"),
...
)either a numeric 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 longitude is missing, both it and
latitude are taken from the built-in coastlineWorld dataset.
numeric vector of latitudes of points to be plotted (ignored if the first argument contains both latitude and longitude).
optional numeric vectors of length two, indicating the
limits of the plot. A warning is issued if these are not specified together.
See “Examples” for a polar-region example, noting that
the whole-globe span of longitudelim is used to centre the plot
at the north pole.
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 of numerical values, NA can be used to
turn off the grid in longitude or latitude. Grids are set up based on
examination of the scale used in middle 10 percent of the plot area, and for
most projections this works quite well. If not, one may set
grid=FALSE and add a grid later with mapGrid().
flag indicating the style of axes. With
geographical=0, the axes are conventional, with decimal degrees as
the unit, and negative signs indicating the southern and western
hemispheres. With geographical=1, the signs are dropped, with axis
values being in decreasing order within the southern and western
hemispheres. With geographical=2, the signs are dropped and the axes
are labelled with degrees, minutes and seconds, as appropriate, and
hemispheres are indicated with letters. With geographical=3, things
are the same as for geographical=2, but the hemisphere indication
is omitted. Finally, with geographical=4, unsigned numbers are used,
followed by letters N in the northern hemisphere, S in the southern,
E in the eastern, and W in the western.
color of the background (ignored).
is a deprecated argument; see oce-deprecated.
color of coastlines and international borders (ignored unless
type="polygon".
either the color for filling polygons (if type="polygon")
or the color of the points and line segments (if type="p",
type="l", or type="o"). If col=NULL then a default
will be set: no coastline filling for the type="polygon" case,
or black coastlines, for type="p", type="l", or
type="o".
logical value indicating whether to trim any coastline elements that lie wholly
outside the plot region. This can prevent e.g. a problem of filling the whole plot area of
an Arctic stereopolar view, because the projected trace for Antarctica lies outside all
other regions so the whole of the world ends up being "land". Setting clip=FALSE
disables this action, which may be of benefit in rare instances in the line connecting
two points on a coastline may cross the plot domain, even if those points are outside
that domain.
indication of type; may be "polygon", for a filled polygon,
"p" for points, "l" for line segments, or "o" for points
overlain with line segments.
a 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. See also axisStyle, lonlabels
and latlabels, which offer more granular control of labelling.
an integer specifying the style of labels for the numbers on axes. The choices are: 1 for signed numbers without additional labels; 2 (the default) for unsigned numbers followed by letters indicating the hemisphere; 3 for signed numbers followed by a degree sign; 4 for unsigned numbers followed by a degree sign; and 5 for signed numbers followed by a degree sign and letters indicating the hemisphere.
character expansion factor for plot symbols,
used if type='p' or any other value that yields symbols.
axis-label expansion factor (see par()).
three-element numerical vector describing axis-label
placement, passed to mapAxis().
logical value indicating whether to draw a box around the plot. This is helpful for many projections at sub-global scale.
logical value indicating whether to show the hemisphere in axis tick labels.
a number indicating the number of degrees of latitude extending from the poles, within which zones are not drawn.
An optional logical value or numeric vector that controls
the labelling along the horizontal axis. There are four possibilities:
(1) If lonlabels is TRUE (the default), then reasonable values are inferred
and axes are drawn with ticks and labels alongside those ticks;
(2) if lonlabels is FALSE, then ticks are drawn, but no labels;
(3) if lonlabels is NULL, then no axis ticks or labels are drawn; and
(4) if lonlabels is a vector of finite numerical values, then tick marks
are placed at those longitudes, and labels are put alongside them.
Note that R tries to avoid overwriting labels on axes, so the instructions
in case 4 might not be obeyed exactly.
See also latlabels, and note that setting axes=FALSE
ensures that no longitude or latitude axes will be drawn regardless
of the values of lonlabels and latlabels.
As lonlabels, but for latitude, on the left
plot axis.
either character value indicating the map projection, or
the output from sf::st_crs(). In the first case, see a table
in “Details” for the projections that are available.
In the second case, note that mapPlot() reports an error if
a similar function from the old sp package is used.
logical value indicating whether to use mapTissot()
to plot Tissot indicatrices, i.e. ellipses at grid intersection points, which
indicate map distortion.
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. It is not a perfect solution, though, because the line segment joining two off-scale points might intersect the plotting box.
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.
The following table lists projections available in oce, and was generated
by reformatting a subset of the output of the unix
command proj -lP. Most of the arguments have default values, and many
projections also have optional arguments. Although e.g. proj -l=aea
provides a little more information about particular projections,
users ought to consult reference 4 for fuller details and illustrations.
| 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 |
| Equal earth | eqearth | - |
| Euler | euler | lat_1, lat_2 |
| Extended transverse Mercator | etmerc | - |
| Fahey | fahey | - |
| Foucault | fouc | - |
| Foucault 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 | - |
| Interrupted Goode homolosine | igh | - |
| Kavraisky V | kav5 | - |
| Kavraisky VII | kav7 | - |
| Lambert azimuthal equal area | laea | - |
| Longitude and latitude | longlat | - |
| Longitude and latitude | latlong | - |
| Lambert conformal conic | lcc | lat_1, lat_2 or lat_0, k_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 | - |
| 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 | - |
| Transverse cylindrical equal area | tcea | - |
| Tissot | tissot | lat_1, lat_2 |
| Transverse Mercator | tmerc | approx |
| 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, approx |
| 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 |
The best choice of projection depends on the application.
Users 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,
merc in limited-area cases where angle preservation is
important, or either aea or eqearth (on local and global
scales, respectively) where area preservation is important.
The choice becomes more important, the larger the size of the region
represented. When it comes to publication, it can be sensible to use the
same projection as used in previous reports.
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.
2020-12-24: complete switch from rgdal to sf,
removing the testing scheme created on 2020-08-03.
2020-08-03: added support for the eqearth projection (like robin but
an equal-area method).
2020-08-03: dropped support for the healpix, pconic
and rhealpix projections, which caused errors with the
sf package. (This is not a practical loss, since these
interrupted projections were handled badly by mapPlot()
in any case.)
2020-08-03: switch from rgdal to sf for
calculations related to map projection, owing to some
changes in the former package that broke oce
code. (To catch problems, oce was set up to use
both packages temporarily, issuing warnings if the results differed
by more than 1 metre in easting or northing values.)
2017-11-19: imw_p removed, because it has problems doing
inverse calculations.
This is a also problem in the standalone PROJ.4 application version
4.9.3, downloaded and built on OSX.
See https://github.com/dankelley/oce/issues/1319 for details.
2017-11-17: lsat removed, because it does not work in
rgdal or in the latest standalone PROJ.4 application.
This is a also problem in the standalone PROJ.4 application version
4.9.3, downloaded and built on OSX.
See https://github.com/dankelley/oce/issues/1337 for details.
2017-09-30: lcca removed, because its inverse was
wildly inaccurate in a Pacific Antarctic-Alaska application
(see https://github.com/dankelley/oce/issues/1303).
Dan Kelley and Clark Richards
The calculations for map projections are done with
the sf package. Importantly, though, not all
the sf projections are
available in oce, for reasons relating to limitations
of sf, for example relating to inverse-projection
calculations. The oce choices are tabulated
below, e.g. projection="+proj=aea" selects the Albers equal area
projection. (See also the warning, below, about a problem
with sf version 0.9-8.)
Further details of the vast array of map projections provided by PROJ
are given in reference 4. This system has been in rapid development
since about 2018, and reference 5 provides a helpful overview of the changes
and the reasons why they were necessary. Practical examples of map projections in
oce are provided in reference 6, along with some notes on problems.
A fascinating treatment of the history of map projections is provided
in reference 7. To get an idea of how projections are being created
nowadays, see reference 8, about the eqearth projection that was added
to oce in August 2020.
Snyder, John P., 1987. Map Projections: A Working Manual. USGS
Professional Paper: 1395
https://pubs.er.usgs.gov/publication/pp1395
Natural Resources Canada
https://www.nrcan.gc.ca/earth-sciences/geography/topographic-information/maps/9805
"List of Map Projections." In Wikipedia, January 26, 2021.
https://en.wikipedia.org/w/index.php?title=List_of_map_projections.
PROJ contributors (2020).
"PROJ Coordinate Transformation Software Library."
Open Source Geospatial Foundation, n.d.
https://proj.org.
Bivand, Roger (2020) Why have CRS, projections and transformations changed?
A gallery of map plots is provided at
https://dankelley.github.io/r/2020/08/02/oce-proj.html
Snyder, John Parr.
Flattening the Earth: Two Thousand Years of Map Projections.
Chicago, IL: University of Chicago Press, 1993.
https://press.uchicago.edu/ucp/books/book/chicago/F/bo3632853.html
Šavrič, Bojan, Tom Patterson, and Bernhard Jenny. "The Equal Earth Map Projection." International Journal of Geographical Information Science 33, no. 3 (March 4, 2019): 454-65. tools:::Rd_expr_doi("10.1080/13658816.2018.1504949")
Points may be added to a map with mapPoints(), lines with
mapLines(), text with mapText(), polygons with
mapPolygon(), images with mapImage(), and scale bars
with mapScalebar(). Points on a map may be determined with mouse
clicks using mapLocator(). Great circle paths can be calculated
with geodGc(). See reference 8 for a demonstration of the available map
projections (with graphs).
Other functions related to maps:
formatPosition(),
lonlat2map(),
lonlat2utm(),
map2lonlat(),
mapArrows(),
mapAxis(),
mapContour(),
mapCoordinateSystem(),
mapDirectionField(),
mapGrid(),
mapImage(),
mapLines(),
mapLocator(),
mapLongitudeLatitudeXY(),
mapPoints(),
mapPolygon(),
mapScalebar(),
mapText(),
mapTissot(),
oceCRS(),
shiftLongitude(),
usrLonLat(),
utm2lonlat()
# NOTE: the map-projection vignette has many more examples.
library(oce)
data(coastlineWorld)
# Demonstrate a high-latitude view using a built-in "CRS" value that is used
# by the National Snow and Ice Data Center (NSIDC) for representing
# the northern-hemisphere ice zone. The view is meant to mimic the figure
# at the top of the document entitled "A Guide to NSIDC's Polar Stereographic
# Projection" at https://nsidc.org/data/user-resources/help-center, with the
# box indicating the region of the NSIDC grid.
library(oce)
data(coastlineWorld)
projection <- sf::st_crs("EPSG:3413")
cat(projection$proj4string, "\n") # see the projection details
par(mar=c(2, 2, 1, 1)) # tighten margins
mapPlot(coastlineWorld, projection=projection,
col=gray(0.9), geographical=4,
longitudelim=c(-180, 180), latitudelim=c(10, 90))
# Coordinates of box from Table 6 of the NSIDC document
box <- cbind(-360+c(168.35,102.34,350.3,279.26,168.35),
c(30.98, 31.37, 34.35, 33.92, 30.98))
mapLines(box[,1], box[,2], lwd=2)
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