将行政区域划分为给定数量的部分

Question

我有以下情节。

我想将行政区域划分为给定数目（例如20）相等的部分。

library(maps)
data(world.cities)

Pakistan <- data.frame(map("world", "Pakistan", plot = FALSE)[c("x","y")])

library(ggplot2)

p <- ggplot(Pakistan, aes(x = x, y = y)) +
     geom_path(colour = 'green', linestyle = 2) +
     coord_map() + 
     theme_bw() + 
      labs(x=" ", y=" ") + 
  theme( 
         panel.grid.minor = element_blank()
      , panel.grid.major=element_blank()
      , axis.ticks = element_blank()
      , axis.text.x = element_blank()
      , axis.text.y = element_blank()
      , panel.border = element_blank()
      )

print(p)

已编辑

我找到了这个

makeVchopper <- function(pol){
    bb = bbox(pol)
    delta = (bb[2,2] - bb[2,1])/10
    xmin = bb[1,1]-delta
    ymin = bb[2,1]-delta
    ymax = bb[2,2]+delta

    choppoly = function(xmax){
        readWKT(sprintf("POLYGON((%s %s, %s %s, %s %s, %s %s, %s %s))",
                        xmin,ymin, xmin,ymax, xmax,ymax, xmax,ymin, xmin,ymin))
    }
    choppoly
}

slicer <- function(pol, xmin, xmax){
    bb = bbox(pol)
    delta = (bb[2,2] - bb[2,1])/10
    ymax = bb[2,2] + delta
    ymin = bb[2,1] - delta
    r = readWKT(sprintf("POLYGON((%s %s, %s %s, %s %s, %s %s, %s %s))",
        xmin,ymin, xmin,ymax, xmax,ymax, xmax,ymin, xmin,ymin))
    gIntersection(pol,r)
}

chop_thirds <- function(pol, fractions=c(1/3, 2/3)){
    chopper = makeVchopper(pol)
    bb = bbox(pol)
    xmin = bb[1,1]
    xmax = bb[1,2]

    totalArea = gArea(pol)

    chopped_area = function(x){
        gArea(gIntersection(chopper(x),pol))
    }

    edges = lapply(fractions, function(fraction){
        target = totalArea * fraction
        target_function = function(x){
            chopped_area(x) - target
        }
        uniroot(target_function, lower=xmin, upper=xmax)$root
    })

    xdelta = (xmax-xmin)/10
    chops = matrix(c(xmin-xdelta, rep(edges,rep(2,length(edges))),
xmax+xdelta), ncol=2, byrow=TRUE)
    apply(chops, 1, function(edges){
        slicer(pol, edges[1], edges[2])
    })

}

# Usage:

library(rgeos)
library(sp)

# sample data
pol <- readWKT("POLYGON((-180 -20, -140 55, 10 0, -140 -60, -180 -20), (-150 -20, -100 -10, -110 20, -150 -20))")
plot(pol)

# now split

parts = chop_thirds(pol)
plot(pol)
plot(parts[[1]], add=TRUE, col=1)
plot(parts[[2]], add=TRUE, col=2)
plot(parts[[3]], add=TRUE, col=3) 

gArea(parts[[1]])
gArea(parts[[2]])
gArea(parts[[3]])