character string naming a geographical database, a list of
x, y, and names obtained from a previous call to
map or a spatial object of class SpatialPolygons or SpatialLines.
The string choices include a world map,
three USA databases (usa, state,
county), and more (type help(package='maps') to see the package index). The
location of the map databases may be overridden by setting the
R_MAP_DATA_DIR environment variable.
regions
character vector that names the polygons to draw.
Each database is composed of a collection of polygons, and each polygon has
a unique name.
When a region is composed of more than one polygon, the individual polygons
have the name of the region, followed by a colon and a qualifier,
as in michigan:north and michigan:south.
Each element of regions is matched
against the polygon names in the database and, according to
exact, a subset is selected for drawing. The regions may also be
defined using (perl) regular expressions. This makes it possible to use
'negative' expressions like "Norway(?!:Svalbard)", which means Norway
and all islands except Svalbard. All entries are case insensitive.
The default selects all polygons in the database.
exact
If TRUE, only exact matches with regions are
selected for drawing.
If FALSE, each element of regions is matched
as a regular expression
against the polygon names in the database and all matches are selected
for drawing.
boundary
If FALSE, boundary segments are not drawn.
A boundary segment is a line segment of the map that bounds only
one of the polygons to be drawn.
This argument is ignored if fill is TRUE.
interior
If FALSE, interior segments are not drawn.
An interior segment is a line segment of the map that bounds two
of the polygons to be drawn.
This argument is ignored if fill is TRUE.
projection
character string that names a map projection to use.
See mapproject (in the mapproj library).
The default is to use a rectangular projection with the aspect ratio
chosen so that longitude and latitude scales are equivalent at the
center of the picture.
parameters
numeric vector of parameters for use with the
projection argument.
This argument is optional only in the sense that certain
projections do not require additional parameters.
If a projection does require additional parameters, these
must be given in the parameters argument.
orientation
a vector c(latitude, longitude, rotation) describing where
the map should be centered and a clockwise rotation (in degrees)
about this center.
fill
logical flag that says whether to draw lines or fill areas.
If FALSE, the lines bounding each region will be drawn (but
only once, for interior lines).
If TRUE, each region will be filled using colors from the
col = argument, and bounding lines will not be drawn.
col
vector of colors.
If fill is FALSE, the first color is used for plotting
all lines, and any other colors are ignored.
Otherwise, the colors are matched one-one with the polygons
that get selected by the region argument (and are reused
cyclically, if necessary).
A color of NA causes the corresponding region to be deleted
from the list of polygons to be drawn.
Polygon colors are assigned after polygons are deleted due to values
of the xlim and ylim arguments.
plot
logical flag that specifies whether plotting
should be done.
If plot is TRUE the return value of map will
not be printed automatically .
add
logical flag that specifies whether to add to the
current plot.
If FALSE, a new plot is begun, and a new coordinate
system is set up.
namesonly
If TRUE, the return value will be a character vector of
the names of the selected polygons. See the Value section below.
xlim
two element numeric
vector giving a range of longitudes, expressed
in degrees, to which drawing
should be restricted.
Longitude is measured in degrees east of Greenwich, so that, in particular,
locations in the USA have negative longitude.
If fill = TRUE, polygons selected by region must be entirely inside
the xlim range.
The default value of this argument spans the entire longitude range
of the database.
ylim
two element
numeric vector giving a range of latitudes,
expressed in degrees, to which drawing
should be restricted.
Latitude is measured in degrees north of the
equator, so that, in particular,
locations in the USA have positive latitude.
If fill = TRUE, polygons selected by region must be entirely inside
the ylim range.
The default value of this argument spans the entire latitude range
of the database.
wrap
If TRUE, lines that cross too far across the map
(due to a strange projection) are omitted.
resolution
number that specifies the resolution with which
to draw the map.
Resolution 0 is the full resolution of the database.
Otherwise, just before polylines are plotted they are thinned:
roughly speaking, successive points on the polyline that are
within resolution device pixels of one another are collapsed
to a single point (see the Reference for further details).
Thinning is not performed if plot = FALSE or when polygons are drawn (fill = TRUE or database is a list of polygons).
type
character string that controls drawing of the map.
Aside from the default type = "l", the value type = "n"
can be used
to set up the coordinate system and projection for a map that will
be added to in later calls.
bg
background color.
mar
margins, as in par. Defaults allow for map.axes().
myborder
scalar or vector of length 2 specifying the porportion of the plot
to add to the defined or computed limits as borders.
namefield
A vector of column names to be used as region name if database is a SpatialPolygonsDataFrame. Ignored in all other cases.
...
Extra arguments passed to polygon or lines. Of particular interest may be the options border andlty that control the color and line type of the polygon borders.
Details
The simplest form of use of this function is:
map(mymap)
where mymap is the returned value from a previous call to
map().
Value
If plot = TRUE, a plot is made where
the polygons selected from database, through the
regions, xlim, and ylim arguments, are outlined
(fill is FALSE) or filled (fill is TRUE)
with the colors in col.
The return value is a list with
x, y, range, and names components.
This object can be used as a database for successive calls
to map and functions.
If fill is FALSE, the x and y vectors are
the coordinates of successive polylines, separated by NAs. If
fill is TRUE, the x and y vectors have
coordinates of successive polygons, again separated by NAs.
Thus the return value can be handed directly to lines or
polygon, as appropriate.
When namesonly is TRUE, only the names component is returned.
After a call to map for which the projection argument was
specified there will be a global variable .Last.projection
containing information about the projection used.
This will be consulted in subsequent calls to map which use
projection = ''.
Richard A. Becker, and Allan R. Wilks,
"Constructing a Geographical Database",
AT&T Bell Laboratories Statistics Research Report [95.2], 1995.http://ect.bell-labs.com/sl/doc/95.2.ps
See Also
map.text, map.axes,
map.scale, map.grid (in the mapproj library),
SpatialPolygons2map
Examples
map() # low resolution map of the world
map('usa') # national boundaries
map('county', 'new jersey') # county map of New Jersey
map('state', region = c('new york', 'new jersey', 'penn')) # map of three states
map("state", ".*dakota", myborder = 0) # map of the dakotas
map.axes() # show the effect of myborder = 0
if(require(mapproj))
map('state', proj = 'bonne', param = 45) # Bonne equal-area projection of states
# names of the San Juan islands in Washington state
map('county', 'washington,san', names = TRUE, plot = FALSE)
# national boundaries in one linetype, states in another
# (figure 5 in the reference)
map("state", interior = FALSE)
map("state", boundary = FALSE, lty = 2, add = TRUE)
# plot the ozone data on a base map
# (figure 4 in the reference)
data(ozone)
map("state", xlim = range(ozone$x), ylim = range(ozone$y))
text(ozone$x, ozone$y, ozone$median)
box()
if(require(mapproj)) { # mapproj is used for projection="polyconic"
# color US county map by 2009 unemployment rate
# match counties to map using FIPS county codes
# Based on J's solution to the "Choropleth Challenge"
# http://blog.revolutionanalytics.com/2009/11/choropleth-challenge-result.html
# load data
# unemp includes data for some counties not on the "lower 48 states" county
# map, such as those in Alaska, Hawaii, Puerto Rico, and some tiny Virginia
# cities
data(unemp)
data(county.fips)
# define color buckets
colors = c("#F1EEF6", "#D4B9DA", "#C994C7", "#DF65B0", "#DD1C77", "#980043")
unemp$colorBuckets <- as.numeric(cut(unemp$unemp, c(0, 2, 4, 6, 8, 10, 100)))
leg.txt <- c("<2%", "2-4%", "4-6%", "6-8%", "8-10%", ">10%")
# align data with map definitions by (partial) matching state,county
# names, which include multiple polygons for some counties
cnty.fips <- county.fips$fips[match(map("county", plot=FALSE)$names,
county.fips$polyname)]
colorsmatched <- unemp$colorBuckets [match(cnty.fips, unemp$fips)]
# draw map
map("county", col = colors[colorsmatched], fill = TRUE, resolution = 0,
lty = 0, projection = "polyconic")
map("state", col = "white", fill = FALSE, add = TRUE, lty = 1, lwd = 0.2,
projection="polyconic")
title("unemployment by county, 2009")
legend("topright", leg.txt, horiz = TRUE, fill = colors)
# Choropleth Challenge example, based on J's solution, see:
# http://blog.revolutionanalytics.com/2009/11/choropleth-challenge-result.html
# To see the faint county boundaries, use RGui menu: File/SaveAs/PDF
}