Add Cities to Existing Map

Adds city locations and (optionally) names to an existing map using a specified database.

Usage

map.cities(x = world.cities, country = "", label = NULL, minpop = 0,
maxpop = Inf, capitals = 0, cex = par("cex"), projection = FALSE,
parameters = NULL, orientation = NULL, pch = 1, ...)

Arguments

x: Name of database. See world.cities to determine the structure of the database. WARNING: should you use this function to plot another set of data points, keep in mind that points on a map can nowadays be localised upto extreme detail with specialized software (a dot on a national map can reveal someones home address), so beware not to reveal private data in some way.
country: If the string country is specified, limit the displayed cities to be from within the specified country, province or state (depending on how the database has been constructed).
label: If TRUE, label all cities. If NULL, the cities will be labelled unless there are 20 or more.
minpop: The minimum value of population below which a particular city will not be shown.
maxpop: The maximum value of population above which a particular city will not be shown.
capitals: Selection of capitals-only display. Capitals may be 1 (country capital), 2 (provincial, state, or regional capital) or 3 (local capital). See world.cities for further information.
cex: The value of cex acts to override the current value of character size expansion.
projection: Boolean or character value. If FALSE (the default), no projection is assumed, if TRUE, the previous projection is used, otherwise a character string that names a map projection to use. See mapproject (in the mapproj library).
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.
pch: plotting character to use for marking city location. See points for options.
...: Further plotting parameters may be specified as for the commands points and text.

Value

No value is returned from map.cities.

Side Effects

All cities within the boundaries of the plot containing the current map are added to the plot. Note that it is possible that the boundaries of the plot exceed the boundaries of the map requested, and so more cities than were expected might be shown.

Details

The database is searched for all cities matching the specified criteria and fitting within the limits of the plot currently displayed. The default database is of all cities that have a population greater than a certain threshold or which are capital cities of a country or island territory. The threshold varies from country to country, but in general is no higher than about 40,000. The data were originally obtained from Stefan Helders' website (http://www.world-gazetteer.com), which no longer exists. There are no recent updates available.

There are three supplied databases, world.cities (the default), us.cities and canada.cities. The latter two, which need to be made available by using a 'data()' call, include the state or province name with the city name (thanks to John Woodruff jpwoodruff@irisinternet.net for the state and province information).

Note that if the underlying map is "Pacific-centric", i.e. longitudes exceed 180 degrees, and a projection is used, then the map.cities data must be transformed appropriately.

Examples

map("world", "China")
map.cities(country = "China", capitals = 2)
map("state", "New Jersey")
data(us.cities)
map.cities(us.cities, country="NJ")