美國和加拿大的彩色網格單元格

Question

我想在美國和加拿大填色網格單元格。我的目標與這個問題非常相似：R Plot Filled Longitude-Latitude Grid Cells on Map但是，這個問題只涉及美國，我無法弄清楚如何添加加拿大。

我能夠通過修改代碼來繪製地圖，美國和加拿大在這裏找到：https://groups.google.com/forum/#!topic/ggplot2/KAKhoE0GO4U

library(ggplot2) 
library(rgeos) 
library(maps) 
library(maptools) 

PolygonCoords <- function(polygon) { 
    polygons <- polygon@Polygons 
    coords.list <- lapply(seq_along(polygons), function(i) { 
    # Extract the group, sequence, area, longitude, and latitude. 
    coords <- polygons[[i]]@coords 
    cbind(i, 1:nrow(coords), polygons[[i]]@area, coords) 
    }) 
    coords.df <- as.data.frame(do.call(rbind, coords.list)) 
    names(coords.df) <- c("order", "seq", "area", "long", "lat") 
    return(coords.df) 
} 

ConvertWorldSimple <- function(mapdata, min.area = 0) { 

    coords.list <- lapply(mapdata@polygons, PolygonCoords) 
    ncoords <- sapply(coords.list, nrow) 
    coords.df <- do.call(rbind, coords.list) 
    coords.df$country <- rep(mapdata@data$NAME, ncoords) 
    country.group <- factor(paste(coords.df$country, coords.df$order)) 
    coords.df$group <- as.numeric(country.group) 
    coords.df <- coords.df[coords.df$area >= min.area, ] 
    return(coords.df) 
} 

data("wrld_simpl") 
world <- ConvertWorldSimple(wrld_simpl, min.area = 0.1) 

world <- world[world$country %in% c('United States', 'Canada'),] 

na <- data.frame(
    country = c("United States", "Canada"), 
    is.north.america = TRUE) 

world <- merge(world, na, all.x = TRUE) 
world$is.north.america[is.na(world$is.north.america)] <- FALSE 

world <- world[order(world$order, world$seq), ] 

ggplot(world, aes(long, lat, group = group)) + 
    geom_polygon(aes(fill = is.north.america)) + 
    geom_path(color = "white", size = 0.1) + 
    scale_fill_manual(values = c("darkgray"), guide = "none") + 
    scale_y_continuous("", breaks=(-2:2) * 30) + 
    scale_x_continuous("", breaks=(-4:4) * 45) + 
    coord_equal() + 
    theme_bw() 

下面是代碼來創建網格單元假屬性數據，發現這裏：http://www.numbertheory.nl/2011/11/08/drawing-polar-centered-spatial-maps-using-ggplot2/

set.seed(1234) 

xlim = c(-110,-100) 
ylim = c(40,60) 

dat_grid = expand.grid(x = xlim[1]:xlim[2], y = ylim[1]:ylim[2]) 
dat_grid$z = runif(nrow(dat_grid)) 

head(dat_grid) 

這裏是在前面的堆棧溢出後用於覆蓋屬性的網格地圖的48個對ggplot2代碼：

library(ggplot2) 
library(maps) 
us_states <- map_data("state") 
(ggplot(aes(x=x,y=y,fill=z),data=dat_grid) + geom_tile())+geom_polygon(data=us_states,aes(x=long, y=lat, group=group), colour="black", fill="white", alpha=0) 

如何結合兩個ggplot語句將假屬性數據網格覆蓋到美國和加拿大的地圖上？感謝您的任何建議。

Answer 1

這應該做的工作

library(ggplot2) 
library(maps) 

us = map_data("state") 
# or this if you don't want the states' boundary 
# us = map_data("states", boundary=FALSE) 
ca = map_data("world", "Canada") 

set.seed(1234) 
xlim = c(-110,-100) 
ylim = c(40,60) 
dat_grid = expand.grid(x = xlim[1]:xlim[2], y = ylim[1]:ylim[2]) 
dat_grid$z = runif(nrow(dat_grid)) 

p = ggplot(aes(x=x,y=y,fill=z),data=dat_grid) 
p + geom_tile() + geom_polygon(data=us,aes(x=long, y=lat, group=group), colour="black", fill="white", alpha=0) + 
    geom_polygon(data=ca,aes(x=long, y=lat, group=group), colour="black", fill="white", alpha=0) 

如果您需要阿拉斯加：

library(ggplot2) 
library(maps) 

m = map_data("world2", c("usa", "Canada")) 

set.seed(1234) 
xlim = c(250,300) 
ylim = c(40,60) 
dat_grid = expand.grid(x = xlim[1]:xlim[2], y = ylim[1]:ylim[2]) 
dat_grid$z = runif(nrow(dat_grid)) 

p = ggplot(dat_grid,aes(x=x,y=y)) + geom_tile(aes(fill=z)) 
p + geom_polygon(data=m,aes(x=long, y=lat, group=group), colour="black", fill="white", alpha=0)