How to filter a shape file before plotting it in R

问题

Just to try to filter a shape file to ease plotting

I have a shape file downloaded from UK gov:

http://geoportal.statistics.gov.uk/datasets/7ff28788e1e640de8150fb8f35703f6e_1/data?geometry=-76.678%2C45.365%2C69.572%2C63.013&orderBy=lad16cd&orderByAsc=false&where=%20(UPPER(lad16cd)%20like%20%27%25E0800000%25%27%20OR%20UPPER(lad16cd)%20like%20%27%25E08000010%25%27)%20

Based on this: https://www.r-bloggers.com/r-and-gis-working-with-shapefiles/

I wrote but do not know to filter :

setwd("~/Documents/filename")
getwd() #  --double confirm real data directory
#install.packages("maptools")
library(maptools)
crswgs84=CRS("+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs")
ukmap=readShapePoly("filename.shp",proj4string=crswgs84,verbose=TRUE)

class(ukmap)
str(ukmap@data)
str(ukmap@polygons[[1]])
ukmap@bbox
# <-- need to do some filterig
plot(ukmap) # as this will take too long and not want to plot whole UK

For example I just want "E06000001" to "E06000020".

(the filename is "Local_Authority_Districts_December_2016_Full_Extent_Boundaries_in_the_UK" not sure how to include it in the program coding quote)

回答1:

You can consider to use the sf package to read the shapefile and plot the data. Filtering the sf object is the same as filtering a data frame.

library(sf)

# Read the sahpefile
ukmap <- st_read("Local_Authority_Districts_December_2016_Full_Extent_Boundaries_in_the_UK.shp")

# Subset the sf object
ukmap_sub <- ukmap[ukmap$lad16cd %in% c("E06000001", "E06000020"), ]

# Plot the boundary of ukmap_sub
plot(st_geometry(ukmap_sub))

If you prefer to work with on SpatialPolygonsDataFrame, we can use the readOGR function from the rgdal package. After that, we can subset the SpatialPolygonsDataFrame like a regular data frame.

library(maptools)
library(rgdal)

ukmap <- readOGR(dsn = getwd(), layer = "Local_Authority_Districts_December_2016_Full_Extent_Boundaries_in_the_UK")

ukmap_sub <- ukmap[ukmap$lad16cd %in% c("E06000001", "E06000020"), ]

plot(ukmap_sub)

来源：https://stackoverflow.com/questions/50110733/how-to-filter-a-shape-file-before-plotting-it-in-r

标签

filtering

shapefile