map {maps}

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 map, three USA databases (usa, state, county), and more (see the package index). The location of the map databases may be overridden by setting the R_MAP_DATA_DIR environment variable. See world for further details.

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 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).

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().

border

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.

Values

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 = ”.