a vector of 4 numbers specifying
limits: c(lon.low, lon.high, lat.low, lat.high).
lim can also be a list with a component named range, such
as the result of map, from which limits are taken.
nx, ny
the desired number of equally-spaced longitude and
latitude lines
labels
logical to indicate if grid lines should be labeled with
longitude/latitude values.
pretty
If TRUE, grid lines will be placed at round numbers.
cex, col, lty, font
passed to arguments to par
...
additional arguments passed to lines and
text, e.g. col to change the color of the grid and
lty to change the line type.
Value
Equally-spaced lines of constant longitude and lines of constant
latitude are superimposed on the current map, using the current projection.
These lines will appear curved under most projections, and give an idea of
how the projection works.
See Also
map
Examples
library(maps)
m <- map("usa", plot=FALSE)
map("usa", project="albers", par=c(39, 45))
map.grid(m)
# get unprojected world limits
m <- map('world', plot=FALSE)
# center on NYC
map('world', proj='azequalarea', orient=c(41, -74, 0))
map.grid(m, col=2)
points(mapproject(list(y=41, x=-74)), col=3, pch="x", cex=2)
map('world', proj='orth', orient=c(41, -74, 0))
map.grid(m, col=2, nx=6, ny=5, label=FALSE, lty=2)
points(mapproject(list(y=41, x=-74)), col=3, pch="x", cex=2)
# center on Auckland
map('world', proj='orth', orient=c(-36.92, 174.6, 0))
map.grid(m, col=2, label=FALSE, lty=2)
points(mapproject(list(y=-36.92, x=174.6)), col=3, pch="x", cex=2)
m <- map('nz')
# center on Auckland
map('nz', proj='azequalarea', orient=c(-36.92, 174.6, 0))
points(mapproject(list(y=-36.92, x=174.6)), col=3, pch="x", cex=2)
map.grid(m, col=2)