如何在美国地图上为海蓝色？ [英] How can I color the ocean blue in a map of the US?

问题描述

我想在图像上绘制美国地图，然后填写海洋。

I would like to draw a map of the US over an image, but then fill in the oceans.

这是我的起点：

library(maps)
library(graphics)
image(x=-90:-75, y = 25:40, z = outer(1:15, 1:15, "+"), 
      xlab = "lon", ylab = "lat")
map("state", add = TRUE)

但我希望大西洋和墨西哥湾能够填充纯色。

But I would like the Atlantic Ocean and Gulf of Mexico to be filled in a solid color.

推荐答案

好问题！这个怎么样？

Good question! How's this?

library(maps)
image(x=-90:-75, y = 25:40, z = outer(1:15, 1:15, "+"), 
      xlab = "lon", ylab = "lat")
map("state", add = TRUE)

library(grid)
outline <- map("usa", plot=FALSE) # returns a list of x/y coords
xrange <- range(outline$x, na.rm=TRUE) # get bounding box
yrange <- range(outline$y, na.rm=TRUE)
xbox <- xrange + c(-2, 2)
ybox <- yrange + c(-2, 2)
# create the grid path in the current device
polypath(c(outline$x, NA, c(xbox, rev(xbox))),
         c(outline$y, NA, rep(ybox, each=2)),
         col="light blue", rule="evenodd")

I在阅读了Paul Murrell（ grid 背后的男人）关于网格路径的最新R-Journal文章之后，我遇到了这个问题的解决方案（pdf here）。

I came across the solution to this problem after reading Paul Murrell's (the man behind grid) recent R-Journal article on grid paths (pdf here).

记住：

这不是你画的，不是你画的-Paul Murrell（R Journal Vol。 4/2）

"It’s Not What You Draw, It’s What You Don’t Draw" -Paul Murrell (R Journal Vol. 4/2)

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