get.canusamex.bds: Obtain map boundaries for Canada, USA, and Mexico

Description

Obtain map boundaries of Canada, USA, and Mexico, including state boundaries, in longitude/latitude.

Usage

get.canusamex.bds()

Arguments

Value

(Canada, USA, Mexico) and state outlines. This matrix has two columns, with longitude in the first column and latitude in the second.

Details

This function depends on the maps and mapdata packages to get the appropriate map boundary lines. The function uses the high-resolution boundaries (“worldHires” database) in the mapdata to find the coastlines and national boundaries for Canada, the USA, and Mexico. Then, it appends the state boundaries (in “state” from the maps package), removing the coastlines and national boundaries so that they don't conflict with the higher-resolution ones (from “worldHires”). This allows the user to draw the national and state boundaries with high-resolution and without with conflicting boundaries yielded by the “world” database. This function is intended to be called by the function get.map.lines.M3.proj; in practice, it would rarely be called directly by the user.

Examples

Run this code

## Set up a plotting region (in longitude/latitude) that includes an
## eastern portion of the Canada/USA border.
plot(c(-82,-67), c(39,49), type="n", xlab="Longitude", ylab="Latitude")
## Superimpose national boundaries from "world" database, which is
## fairly low-resolution (since it includes worldwide national boundaries).
map("world", regions="canada", add=TRUE)
## Now, if we try to superimpose the the USA state boundaries from the
## higher resolution "state" database, we have a conflict.  (See
## particularly the Maine border.)
map("state", add=TRUE, col="blue")
## The high-resolution national boundaries in database "worldHires" (in
## mapdata) also don't match up with the state lines.
map("worldHires", add=TRUE, col="magenta")

## Instead, we get the national boundaries (Canada, USA, Mexico) at
## high-resolution from database "worldHires" and the state boundaries
## (without the coastlines and national boundaries) from the "state"
## database.
dev.new()
plot(c(-82,-67), c(39,49), type="n", xlab="Longitude", ylab="Latitude")
lines(get.canusamex.bds())