Draw a latitude/longitude grid on a projected map
Draws a grid on an existing map.
map.grid(lim, nx=9, ny=9, labels=TRUE, pretty=TRUE, cex, col, lty, font, ...)
lim |
a vector of 4 numbers specifying
limits: |
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 |
cex, col, lty, font |
passed to arguments to |
... |
additional arguments passed to |
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.
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)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.