如何将shapefile裁剪为R中的特定集？

Question

我有英国的shapefile，但我只想要英格兰和威尔士。这是我到目前为止使用的代码：

RG <- readOGR("filepath", "filename")
UK <- grep("England", "Wales", RG$NAME_1)
RG_EW <- RG[UK]
plot(RG_EW)

但我仍然以整个英国为终结者。我使用从http://www.gadm.org/下载的shapefile

由于

Answer 1

如果名称是明确的，你只需要选择两个，我只会使用单行而不是grep：

e.w.shp <- uk.shp[uk.shp$NAME_1 == "England" | uk.shp$NAME_1 == "Wales", ]

结果如下：

> str(e.w.shp)
Formal class 'SpatialPolygonsDataFrame' [package "sp"] with 5 slots
  ..@ data       :'data.frame': 134 obs. of  11 variables:
  .. ..$ ID_0     : int [1:134] 239 239 239 239 239 239 239 239 239 239 ...
  .. ..$ ISO      : chr [1:134] "GBR" "GBR" "GBR" "GBR" ...
  .. ..$ NAME_0   : chr [1:134] "United Kingdom" "United Kingdom" "United Kingdom" "United Kingdom" ...
  .. ..$ ID_1     : int [1:134] 1 1 1 1 1 1 1 1 1 1 ...
  .. ..$ NAME_1   : chr [1:134] "England" "England" "England" "England" ...
  .. ..$ ID_2     : int [1:134] 1 2 3 4 5 6 7 8 9 10 ...
  .. ..$ NAME_2   : chr [1:134] "Barking and Dagenham" "Bath and North East Somerset" "Bedfordshire" "Berkshire" ...
  .. ..$ NL_NAME_2: chr [1:134] NA NA NA NA ...
  .. ..$ VARNAME_2: chr [1:134] NA NA NA NA ...
  .. ..$ TYPE_2   : chr [1:134] "London Borough" "Unitary Authority" "Administrative County" "County" ...
  .. ..$ ENGTYPE_2: chr [1:134] "London Borough" "Unitary Authority" "Administrative County" "County" ...
  ..@ polygons   :List of 134

因此使用ggplot2而不是基础图形的完整工作示例可能是这样的：

library(rgdal)
library(ggplot2)
library(rgeos)

shape.dir <- "your_directory_name" # use your directory name here
uk.shp <- readOGR(shape.dir, layer = "GBR_adm2")
e.w.shp <- uk.shp[uk.shp$NAME_1 == "England" | uk.shp$NAME_1 == "Wales", ]
e.w.df <- fortify(e.w.shp, region = "ID_2") # convert to data frame for ggplot

ggplot(e.w.df, aes(x = long, y = lat, group = group)) +
    geom_polygon(colour = "black", fill = "grey80", size = 0.5) +
    theme()

Answer 2

首先，您的grep来电不正确。如果您正在寻找包含“英格兰”或“威尔士”的字符串，您应该这样做：

UK <- grep("(England|Wales)", RG$NAME_1)

然后您可以使用以下内容对数据进行分组：

RG_EW <- RG[UK,]

你终于得到了：

plot(RG_EW)