CODEWITHSUNDEEP
rshapefile
user2021413
user2021413

Reputation: 1

How do I crop a shapefile to a specific set in R?

I have a shapefile for the UK but I only want England and Wales. Here is the code I've used so far:

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

But I still end up with the whole of the UK. I'm using a shapefile downloaded from http://www.gadm.org/

Thanks

Upvotes: 0

Views: 1091

Answers (2)

SlowLearner
SlowLearner

Reputation: 7997

If the names are unambiguous and you only need to select two, I would just use a one-liner rather than use grep:

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

And the result looks like this:

> 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

So a fully worked example using ggplot2 rather than base graphics might go something like this:

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()

screenshot

Upvotes: 2

juba
juba

Reputation: 49033

First, your grep call is incorrect. If you are looking for strings containing either "England" or "Wales" you should do :

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

And then you can subset your data with :

RG_EW <- RG[UK,]

And you finally get :

plot(RG_EW)

enter image description here

Upvotes: 1

Related Questions