ONS-open-geography.Rmd
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Tom Rushby authoredTom Rushby authored
title: "Using the ONS Open Geography API"
subtitle: "example of using the API to get feature layer data - boundaries"
author: "Tom Rushby (@tom_rushby)"
date: 'Last run at: `r Sys.time()`'
output:
bookdown::pdf_document2:
toc: yes
fig_caption: yes
number_sections: yes
bookdown::html_document2:
fig_caption: yes
code_folding: hide
number_sections: yes
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toc_depth: 4
toc_float: TRUE
bookdown::word_document2:
fig_caption: yes
number_sections: yes
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fig_width: 5
always_allow_html: yes
# you might need to install these first
library(sf)
library(htmltools)
library(leaflet)
library(utils)
library(dplyr)
Introduction
This script provides an example of downloading and importing administrative boundaries from the Office for National Statistics Open Geography portal into RStudio and plotting on a map. It is based upon a useful example by Trafford Data Lab.
Creating a query
In this example we want to load Local Authority District geography. The Open Geography portal helpfully provides an API explorer to help us structure the query.
In the code chunk below, we break up the query into parts that we can change depending on the type of geography we want, the areas we want to include, the fields we want the query to return etc.
# Elements for the query
geo_endpoint <- "https://ons-inspire.esriuk.com/arcgis/rest/services/"
# The geo boundary layer will change depending on which
geo_boundarylayer <- "Administrative_Boundaries/Local_Authority_Districts_December_2020_UK_BGC/"
geo_server <- "FeatureServer/0/"
geo_search <- "LAD20NM IN "
# Construct a vector of local authorities to load
# the following local authorities are the 'Solent' region
las_to_load <- c("Southampton","Portsmouth","Winchester",
"Eastleigh","Isle of Wight","Fareham",
"Gosport","Test Valley","East Hampshire",
"Havant","New Forest","Hart","Basingstoke and Deane")
geo_where <- las_to_load # sometimes we don't want all boundaries
geo_outfields <- "*" # returns all fields
#geo_outfields <- c("LAD20CD","LAD20NM","LONG","LAT") # use in place of line above to return selected fields only
geo_outSR <- "4326"
geo_format <- "json"
We then paste the elements together to construct the API query URL ...
# Assemble the full URL for the query from elements above
geo_query_string <- paste0(geo_endpoint,geo_boundarylayer,geo_server,
"query?where=",geo_search,"(",paste(paste0("'",geo_where,"'"), collapse = ","),
")&outFields=",(paste(geo_outfields, collapse = ",")),"&outSR=",geo_outSR,"&f=",geo_format)
# Format the URL to remove spaces
geo_query <- utils::URLencode(geo_query_string)
message("Loading LA geometry from ONS Open Geography API")
# API query
sf_data <- st_read(geo_query)
Checking coordinate reference system
Useful lookup spatial reference for CRS https://spatialreference.org/.
Sometimes transformation is required using the st_transform()
function.
st_coord_sys <- st_crs(sf_data) # check coord system
st_coord_sys # current coord system EPSG: 4326 (is what leaflet wants - good)
# transform the coord system if required
if(st_coord_sys$epsg != 4326){
sf_data <- st_transform(sf_data, "+proj=longlat +datum=WGS84")
}
Create map
Now we can create a map, here using the Leaflet package.
Find a cheatsheet here.
Optional: first we can create popups by adding a column to sf_data
(uses htmltools
).
sf_data$popup_text <-
paste("Locial authority area code: ","<b>", sf_data$lad20cd, "</b>",
'<br/>', 'Local authority: ', '<b>', sf_data$lad20nm, '</b>', ' ') %>%
lapply(htmltools::HTML)
Finally we can create the map ...
leaflet(sf_data) %>%
addTiles() %>% # Add default OpenStreetMap map tiles
addPolygons(color = "blue", fillColor = "blue", fillOpacity = 0.2, weight = 1.5, popup = ~(lad20nm), # popups clicked
label = ~(popup_text), # define labels
labelOptions = labelOptions( # label options
style = list("font-weight" = "normal", padding = "2px 2px"),
direction = "auto"),
highlight = highlightOptions(
weight = 5,
color = "#666",
fillOpacity = 0.7,
bringToFront = TRUE))