map

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Percentile

Draw Geographical Maps

Draw lines and polygons as specified by a map database.

Keywords
hplot
Usage
map(database = "world", regions = ".", exact = FALSE, boundary = TRUE,
  interior = TRUE, projection = "", parameters = NULL, orientation = NULL,
  fill = FALSE, col = 1, plot = TRUE, add = FALSE, namesonly = FALSE,
  xlim = NULL, ylim = NULL, wrap = FALSE, resolution = if(plot) 1 else 0,
  type = "l", bg = par("bg"), mar = c(4.1, 4.1, par("mar")[3], 0.1),
  myborder = 0.01, ...)
Arguments
database
character string naming a geographical database, or a list of x, y, and names obtained from a previous call to map. The string choices include a world<
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 r
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 m
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 s
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,
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
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 regi
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 longit
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
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 a
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.
...
Extra arguments passed to polygon or lines.
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 = ''.

References

Richard A. Becker, and Allan R. Wilks, "Maps in S", AT&T Bell Laboratories Statistics Research Report [93.2], 1993. http://public.research.att.com/areas/stat/doc/93.2.ps

Richard A. Becker, and Allan R. Wilks, "Constructing a Geographical Database", AT&T Bell Laboratories Statistics Research Report [95.2], 1995. http://public.research.att.com/areas/stat/doc/95.2.ps

See Also

map.text, map.axes, map.scale, map.grid (in the mapproj library)

Aliases
  • map
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 matching FIPS codes
  # works much better than trying to match the state, county names
  # which also include multiple polygons for some counties
  colorsmatched <- unemp$colorBuckets [match(county.fips$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
}
Documentation reproduced from package maps, version 2.3-2, License: GPL-2

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