在 ggplot2 中绘制地图时避免水平线和疯狂的形状

Question

我想要一个区域的绘图，例如拉丁美洲，使用 IPUMSI 的世界形状文件...

https://international.ipums.org/international/resources/gis/IPUMSI_world.zip

...我以后会添加更多的IPUMS区所以我真的很想用这个作为我的模板层

当我在 ggplot2 中通过 coord_map 添加限制时，我对情节有困难。

初始空间文件看起来不错

library("ggplot2")
library("raster")

sd0 <- readShapePoly("./IPUMSI_world.shp")
df0 <- fortify(sd0)

ggplot(data = df0, mapping = aes(x = long, y = lat, group = group)) +
  geom_polygon(fill = "black", colour = "black")

当我想关注拉丁美洲时，我看到了一些不需要的水平线：

ggplot(data = df0, mapping = aes(x = long, y = lat, group = group)) +
  geom_polygon(fill = "black", colour = "black") +
  coord_map(xlim = c(-125, -30), ylim = c(-60, 35))

我尝试按照 here

的指导使用 clipPolys 函数修复此问题

library("PBSmapping")
df1 <- df0
names(df1)[c(1,2,6,3)] <- c("X","Y","PID","POS")
df1$PID <- as.numeric(df1$PID)
df2 <- clipPolys(polys = df1, xlim = c(-125, -30), ylim = c(-60, 35), keepExtra = TRUE)
names(df2)[names(df2)=="X"] <- "long" 
names(df2)[names(df2)=="Y"] <- "lat"
names(df2)[names(df2)=="PID"] <- "id"

ggplot(data = df2, mapping = aes(x = long, y = lat, group = group)) +
  geom_polygon(fill = "black", colour = "black")

对这个情节也不是很满意。我认为这是孔的问题，如 question 所示，但建议的解决方案产生与上面相同的图：

gghole <- function(fort){
  poly <- fort[fort$id %in% fort[fort$hole,]$id,]
  hole <- fort[!fort$id %in% fort[fort$hole,]$id,]
  out <- list(poly,hole)
  names(out) <- c('poly','hole')
  return(out)
} 

ggplot(df2, aes(x=long, y=lat, group=group)) +
  geom_polygon(data = gghole(df2)[[1]], fill = "black", colour = "black") +
  geom_polygon(data = gghole(df2)[[2]], fill = "black", colour = "black")

ggplot(df0, aes(x=long, y=lat, group=group)) +
  geom_polygon(data = gghole(df0)[[1]], fill = "black", colour = "black") +
  geom_polygon(data = gghole(df0)[[2]], fill = "black", colour = "black") +
  coord_map(xlim = c(-125, -30), ylim = c(-60, 35))

Answer 1

您应该删除绘图区域之外的数据。因此，使用 scale_x/y_continuous 而不是 coord_map

来设置限制

ggplot(data = df0, mapping = aes(x = long, y = lat, group = group)) +
  scale_x_continuous(limits = c(-125, -30)) +
  scale_y_continuous(limits = c(-60, 35)) +
  geom_polygon(fill = "black", colour = "black")

Answer 2

另一个解决方案是限制视图，而不是从渲染中移除点：

library(ggplot2)
library(maptools)
library(mapproj)

# Maptools dataset
data(wrld_simpl)
world <- fortify(wrld_simpl)

# Same plot, but restrict the view instead of removing points
# allowing the complete render to happen
ggplot(world, mapping = aes(x = long, y = lat, group = group)) +
  geom_polygon(fill = "black", colour = "black") +
  coord_cartesian(xlim = c(-125, -30), ylim = c(-60, 35))

在 ggplot2 中绘制地图时避免水平线和疯狂的形状

Avoiding hoizontal lines and crazy shapes when plotting maps in ggplot2

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ggplot2