Friday, September 10, 2021

R packages for working with shapefile

 A shapefile (points, lines, and polygons) can be read into R object using any of the following packages: sf, rgdal, maptools and PBSmapping.

First you need to install them as follow: install.packages(c('sf', 'rgdal', 'maptools', 'PBSmapping'))

The code below shows how to each package to read in shapefile into an object for further processing.


# read in shapefiles using 'sf'
my_map <- st_read("C:/Users/Yusuf_08039508010/Desktop/Working_Files/2021/08-August/R Poor and Vulnerable/SHP/NIG_ADM.shp")

# read in shapefiles using 'rgdal'
my_map <- readOGR("C:/Users/Yusuf_08039508010/Desktop/Working_Files/2021/08-August/R Poor and Vulnerable/SHP", "NIG_ADM")

# read in shapefiles using 'maptools'
# my_map1 <- readShapePoints("...")
# my_map2 <- readShapeLines("...")
my_map3 <- readShapePoly("C:/Users/Yusuf_08039508010/Desktop/Working_Files/2021/08-August/R Poor and Vulnerable/SHP/NIG_ADM")

# read in shapefiles using 'PBSmapping'
my_map <- importShapefile("C:/Users/Yusuf_08039508010/Desktop/Working_Files/2021/08-August/R Poor and Vulnerable/SHP/NIG_ADM")

Note that using maptools is deprecated and you will get a warning message that reads: readShapePoly is deprecated; use rgdal::readOGR or sf::st_read 

For more, read the web archive on Read and write ESRI Shapefiles with R.

Manipulating spatial data using the SF package

By far, the sf package is commonly used for reading and manipulating shapefiles and other spatial file types such as geojson, geopackage etc. Lets see more on the library(sf)

The package sf tries to fill this gap, and aims at succeeding sp in the long term. Which means sf was developed base on sp which is now deprecated.

In the code snippet below, you will see:-

  1. Using the sf st_read() function to read different spatial files
  2. Converting the sf object to old school sp object and vis-à-vis
  3. Looking at common tidyverse functions that works on sf spatial objects

# Function to create spatial obj. with sp package: st_point(), st_linestring(), and st_polygon()
# However, the function "st_read()" is mostly used to read existing spatial objects

# Read shp...
myMap_1 <- st_read(dsn = "C:/Users/Yusuf_08039508010/Desktop/Working_Files/Fiverr/2021/010-October/NIG Grid/Oyo/NIG.shp")

# Read geoJSON file...
myMap_2 <- st_read("C:/Users/Yusuf_08039508010/Desktop/ng_State.geojson")

# Read GeoPackage (.gpkg) file...
myMap_3 <- st_read("C:/Users/Yusuf_08039508010/Desktop/Working_Files/GIS Data/NGR/GRID3 Data/GPKG files/Fire Stations/fire-stations (5).gpkg")

# What to use sp package...?
# Coverting form "sf data.frame" to sp package i.e: SpatialPointsDataFrame/SpatialLinesDataFrame/SpatialPolygonsDataFrame
class(myMap_1) # This returns sf df...
myMap_1_sp <- as(myMap_1, "Spatial")

# inspect the structure...
str(myMap_1_sp, max.level=2)

# We can see there are five slots, which can be accessed using @ symbol follow by the name

# To convert back to sf, use this function...
myMap_1 <- st_as_sf(myMap_1_sp)
class(myMap_1) # Now we have our sf df, which is the best for working in tydiverse universe.

# Now normal functions in tydiverse will work on the sf df apart from the core spatial functions such as: st_geometry_type(), st_dimension(), st_bbox() and st_crs().
# sf spatial functions....

# tidyverse functions....

That is it!

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