OSapiR

Example R code and a work-in-progress R wrapper for Ordnance Survey APIs

Sign Up

Sign up at https://osdatahub.os.uk/ - free access to OS OpenData APIs and up to £1000 of premium data per calendar month.
Create a new project
Add the OS Maps API to your new project (for the basic and advanced examples below)
Add the OS Features API to your project (for the advanced example below - requires access to premium data)
Copy the 'Project API Key'

Authentication

Good practice in secure authentication is to set your API credentials as a System Environment variable.
Replace the 'xxx...' with your copied Project API Key and run this code.

Sys.setenv(OS_PROJECT_API_KEY = 'xxxxxxxxxxxxxxxxxxxxxxxx')

Or, add OS_PROJECT_API_KEY=xxxxxxxxxxxxxxxxxxxxxxxx (note no quotes) to your .Renviron file to persist the key between sessions.
See https://bookdown.org/csgillespie/efficientR/set-up.html#r-startup for more info on .Renviron

Basic example: Adding backdrops or base map tiles to leaflet maps

Leaflet is one of the most popular open-source JavaScript libraries for interactive maps.
The 'leaflet' package makes it easy to integrate and control Leaflet maps in R.
You can bring in OS map tiles by providing a custom URL template to the addTiles() function.

library(leaflet)

m <- leaflet() %>%
  addTiles(paste0("https://api.os.uk/maps/raster/v1/zxy/Light_3857/{z}/{x}/{y}.png?key=",Sys.getenv("OS_PROJECT_API_KEY"))) %>% 
  addMarkers(lng=-1.470770, lat=50.938039, popup="Explorer House, home of Ordnance Survey")
m  # Print the map

Varying map tile styles

#Define url templates for the different tile styles
OSLight_3857 <- paste0("https://api.os.uk/maps/raster/v1/zxy/Light_3857/{z}/{x}/{y}.png?key=",Sys.getenv("OS_PROJECT_API_KEY"))
OSRoad_3857 <- paste0("https://api.os.uk/maps/raster/v1/zxy/Road_3857/{z}/{x}/{y}.png?key=",Sys.getenv("OS_PROJECT_API_KEY"))
OSOutdoor_3857 <- paste0("https://api.os.uk/maps/raster/v1/zxy/Outdoor_3857/{z}/{x}/{y}.png?key=",Sys.getenv("OS_PROJECT_API_KEY"))

#Pass these templates to the addTiles() function
m <- leaflet() %>%
  addTiles(OSLight_3857) %>% 
  addMarkers(lng=-1.470770, lat=50.938039, popup="Explorer House, home of Ordnance Survey")
m  # Print the map

m <- leaflet() %>%
  addTiles(OSRoad_3857) %>% 
  addMarkers(lng=-1.470770, lat=50.938039, popup="Explorer House, home of Ordnance Survey")
m  # Print the map

m <- leaflet() %>%
  addTiles(OSOutdoor_3857) %>% 
  addMarkers(lng=-1.470770, lat=50.938039, popup="Explorer House, home of Ordnance Survey")
m  # Print the map

Changing the map projection

Leaflet expects all point, line, and shape data to be specified in latitude and longitude using WGS 84 (a.k.a. EPSG:4326).
By default, when displaying this data it projects everything to EPSG:3857 and expects that any map tiles are also displayed in EPSG:3857.
However, you can use custom projections via the integrated Proj4Leaflet plugin.
For more detail on custom projections, see https://rstudio.github.io/leaflet/projections.html

#Define a Proj4Leaflet coordinate reference system (crs) instance configured for British National Grid (EPSG:27700) and the resolutions of our base map
crs <- leafletCRS(crsClass = "L.Proj.CRS", code = "EPSG:27700",
                  proj4def = '+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +towgs84=446.448,-125.157,542.06,0.15,0.247,0.842,-20.489 +units=m +no_defs',
                  resolutions = c(896.0, 448.0, 224.0, 112.0, 56.0, 28.0, 14.0, 7.0, 3.5, 1.75 ),
                  origin = c(-238375.0, 1376256.0)
                  )

#Define url templates for the different tile styles in EPSG:27700 
OSRoad_27700 <- paste0("https://api.os.uk/maps/raster/v1/zxy/Road_27700/{z}/{x}/{y}.png?key=",Sys.getenv("OS_PROJECT_API_KEY"))
OSLight_27700 <- paste0("https://api.os.uk/maps/raster/v1/zxy/Light_27700/{z}/{x}/{y}.png?key=",Sys.getenv("OS_PROJECT_API_KEY"))
OSOutdoor_27700 <- paste0("https://api.os.uk/maps/raster/v1/zxy/Outdoor_27700/{z}/{x}/{y}.png?key=",Sys.getenv("OS_PROJECT_API_KEY"))
OSLeisure_27700 <- paste0("https://api.os.uk/maps/raster/v1/zxy/Leisure_27700/{z}/{x}/{y}.png?key=",Sys.getenv("OS_PROJECT_API_KEY"))

#Pass these templates to the addTiles() function, along with the new crs
m <- leaflet(options=leafletOptions(crs=crs)) %>%
  addTiles(OSRoad_27700) %>% 
  addMarkers(lng=-1.470770, lat=50.938039, popup="Explorer House, home of Ordnance Survey")
m  # Print the map

m <- leaflet(options=leafletOptions(crs=crs)) %>%
  addTiles(OSOutdoor_27700) %>% 
  addMarkers(lng=-1.470770, lat=50.938039, popup="Explorer House, home of Ordnance Survey")
m  # Print the map

m <- leaflet(options=leafletOptions(crs=crs)) %>%
  addTiles(OSLight_27700) %>% 
  addMarkers(lng=-1.470770, lat=50.938039, popup="Explorer House, home of Ordnance Survey")
m  # Print the map

#I've added a max zoom parameter here, given the scale limitation for the OpenData Leisure tiles   
m <- leaflet(options=leafletOptions(crs=crs)) %>%
  addTiles(OSLeisure_27700,options=tileOptions(maxZoom = 5)) %>% 
  addMarkers(lng=-1.470770, lat=50.938039, popup="Explorer House, home of Ordnance Survey")
m  # Print the map

More advanced example: Show features of a given type within the map bounds

The code below creates a simple Shiny web application with an interactive leaflet map.
As you move the map around, the app queries the OS Features API for a specific feature type - Airports.
These are added to the map as polygons.

library(shiny) #Interactive R applications
library(leaflet) #Wrapper for the popular javascript mapping library 
library(httr) #Functions for working with http
library(sf) #Functions for handling geospatial data - simple features

#Set custom url template for OS map for backdrop
OSRoad_3857 <- paste0("https://api.os.uk/maps/raster/v1/zxy/Road_3857/{z}/{x}/{y}.png?key=",Sys.getenv("OS_PROJECT_API_KEY"))
#Base URL for web feature service
wfsServiceUrl <- "https://api.os.uk/features/v1/wfs"

#Define app front-end
ui <- fluidPage(
  #Style map to fill the screen
  tags$style(type = "text/css", "#map {height: calc(100vh) !important;}"),
  #Show the map
  leafletOutput("map")
)

#Define app server functions
server <- function(input, output, session) {
  
  #Show the base map
  output$map <- renderLeaflet({
    leaflet() %>%
      addTiles(OSRoad_3857) %>% setView(lng=-1.470770, lat=50.938039,zoom=12)
  })

  #Create a reactive element that updates when the map is moved
  coords <- reactive(coordinates <- paste0(input$map_bounds$south,",",input$map_bounds$west," ",
                            input$map_bounds$north,",",input$map_bounds$east))  
  observe({
    #When map moves, update the boundary coordinates
    #Could add a strategy to only search in new bounds areas, but keeping it simple for now
    if(coords()!=", ,") {
    #Create an OGC XML filter parameter value which will select features intersecting the bounds coordinates
    # where the site function equals "Airport" 
    xml <- paste0('<ogc:Filter>',
                  '<ogc:And>',
                  '<ogc:BBOX>',
                  '<ogc:PropertyName>SHAPE</ogc:PropertyName>',
                  '<gml:Box srsName="urn:ogc:def:crs:EPSG::4326">',
                  '<gml:coordinates>',coords(),'</gml:coordinates>',
                  '</gml:Box>',
                  '</ogc:BBOX>',
                  '<ogc:PropertyIsEqualTo>',
                  '<ogc:PropertyName>SiteFunction</ogc:PropertyName>',
                  '<ogc:Literal>Airport</ogc:Literal>',
                  '</ogc:PropertyIsEqualTo>',
                  '</ogc:And>',
                  '</ogc:Filter>')
    #Define (WFS) parameters object.
    wfsParams <- paste0("key=",Sys.getenv("OS_PROJECT_API_KEY"),
                        "&service=WFS&request=GetFeature&version=2.0.0&typeNames=Sites_FunctionalSite&outputFormat=GeoJSON&srsName=EPSG:27700",
                        "&filter=",xml)
    #Define query url
    url <-  paste0(wfsServiceUrl,"?",wfsParams)
    #Query api and convert geojson to spatial features 
    sf <- read_sf(GET(url),crs=27700,as_tibble=F)
    #Set CRS for standard web mapping (convert from national grid to degrees)
    sfw <- st_transform(sf,4326)
    #Finally update map
    leafletProxy("map") %>% clearShapes() %>% addPolygons(data=sfw)
    }
  })
}

#Launch the app
shinyApp(ui, server)

howaskew / OSapiR