13. A New Tool - Is It In London?

There are some places that lie within the M25 but are not in any London Borough. TFL might operate some buses in these areas, you might be able to use a London Underground station, but you won’t be able to vote in London elections. Depending on your point of view (usually where you live), these places might be ‘in London’ or they might not.

This map shows the area within the M25 that is not part of any London Borough. To build this, I used a bunch of new geometry tools and:

# Let's loadng the sf and mapview libraries to process and view geospatial data
library(sf)
library(leaflet)
library(raster)
library(terra)
library(concaveman)

# Load the M25 and A282 roads
m25 <- st_read('./data/13/Data/oproad_gb.gpkg', quiet = TRUE, query = 'select * from road_link where (road_classification_number = "M25" or road_classification_number = "A282")')

# Load the London Wards shapefile
london_wards <- st_read('./data/13/London-wards-2018_ESRI/London_Ward.shp', quiet = TRUE)

# Combine the M25 and A282 roads to form a continuous path
m25_coords <- st_union(m25) %>% st_cast('POINT') %>% st_union() %>% st_coordinates()

# Use concaveman to create a concave hull around the points
polygon_boundary <- concaveman(m25_coords)

# Convert the concave hull back to an sf polygon
m25_poly <- st_sfc(st_polygon(list(polygon_boundary)), crs = 27700)

# Subtract the London Wards from the M25 polygon
inside_m25_outside_london <- st_difference(m25_poly, st_union(london_wards))

# The bounds of the UK in EPSG:27700
minx <- 0
miny <- 0
maxx <- 700000
maxy <- 1300000

# Create a rectangle vector
rect <- st_sfc(st_polygon(list(rbind(c(minx, miny), c(maxx, miny), c(maxx, maxy), c(minx, maxy), c(minx, miny)))), crs=27700)

# Punch a hole in the rectangle using the M25 polygon
m25_hole <- st_difference(rect, inside_m25_outside_london) %>% st_transform(crs=4326)

# Create a leaflet map
map <- leaflet(width = "100%") %>%
  addProviderTiles("OpenStreetMap.Mapnik") %>%
  addPolygons(
    data = m25_hole,
    color = "white",
    fillColor = "white",
    fillOpacity = 0.95
  )%>%
  setView(lng = -0.1407376, lat = 51.4908968, zoom = 10) 

map

13. A New Tool - Is It In London?

Credits