Index map regions

View source: R/db.r

match.mapR Documentation

Index map regions


Assigns an index to each map region, useful for map coloring.

Usage, regions, exact = FALSE, warn = TRUE)



character string naming a geographical database, or a map object. See the documentation for map for more details.


a vector of names, or more generally regular expressions to match against the map region names.


If TRUE, only exact matches with regions are considered. Otherwise each element of regions is assumed to be a regular expression. Matches are always case-insensitive.


If TRUE, a warning is printed when an element of regions matches nothing in the map.


Returns an integer vector giving an index to each region in the database. The index is the index of the string in regions which matches the region name. Matching is done as in map. More specifically, all regions r whose name matches regions[i] will have index i. Unmatched regions will have index NA. Overlapping matches cause an error.

This behavior differs from pmatch because a single entry in regions may match several entries in the map.


Tom Minka


Richard A. Becker, and Allan R. Wilks, "Maps in S", AT&T Bell Laboratories Statistics Research Report, 1991.

See Also



# filled map showing Republican vote in 1900
# (figure 6 in the reference)
data(state, package = "datasets")
data(votes.repub) <-"state",
x <- votes.repub[, "1900"]
gray.colors <- function(n) gray(rev(0:(n - 1))/n)
color <- gray.colors(100)[floor(x)]
map("state", fill = TRUE, col = color); map("state", add = TRUE)

maps documentation built on May 29, 2024, 9:04 a.m.