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Codes postaux

Michael发表于 2024-11-30 11:00:00

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Yellow post box – CC-BY-SA by Elliott Brown

Day 30 of 30DayMapChallenge: « The final map » (previously).

Creating a raw polygon layer of french postal codes from points

This data, although not a “real” administrative limit, is often used in many different applications, see for example the BNV-D.

There is no free, up-to-date, layer of polygon boundaries for french postal codes.

The official database is just a table giving a postal code for each commune code, optionally with point coordinates. We have some postal codes shared by several communes and some communes have several postal codes (at the same point location).
Using the national address base (BAN) we can compute the convex hulls: Contours calculés des zones codes postaux. Interesting method but old (2021) and with many holes/overlaps
Fond de carte des codes postaux is nice (although métropole only) but old (2013).

Config

library(readr)
library(dplyr)
library(tidyr)
library(stringr)
library(purrr)
library(ggplot2)
library(glue)
library(janitor)
library(sf)

Data

# Postal codes as point by commune
cp_points <- read_csv("https://datanova.laposte.fr/data-fair/api/v1/datasets/laposte-hexasmal/metadata-attachments/base-officielle-codes-postaux.csv",
                      name_repair = make_clean_names) |> 
  separate(geopoint, into = c("lat", "lon"), sep = ",", convert = TRUE) |> 
  drop_na(lon, lat) |> 
  st_as_sf(coords = c("lon", "lat"), crs = "EPSG:4326") |> 
  filter(str_sub(code_commune_insee, 1, 3) < "987") |> 
  mutate(proj = case_when(str_sub(code_commune_insee, 1, 3) %in% c("971", "972", "977", "978") ~ "EPSG:5490",
                          str_sub(code_commune_insee, 1, 3) == "973" ~ "EPSG:2972",
                          str_sub(code_commune_insee, 1, 3) == "974" ~ "EPSG:2975",
                          str_sub(code_commune_insee, 1, 3) == "976" ~ "EPSG:4471",
                          .default = "EPSG:2154"))

# France limits, to clip voronoi polygons
fr <- read_sf("https://static.data.gouv.fr/resources/admin-express-cog-simplifiee-2024-metropole-drom-saint-martin-saint-barthelemy/20240930-094021/adminexpress-cog-simpl-000-2024.gpkg",
              layer = "departement") |> 
  mutate(terr = if_else(insee_reg > "06", "fx", insee_reg)) |> 
  group_by(terr) |> 
  summarise()

# Communes limits and population to give the name of the postal code as the 
# biggest commune (by pop)
com <- read_sf("https://static.data.gouv.fr/resources/admin-express-cog-simplifiee-2024-metropole-drom-saint-martin-saint-barthelemy/20240930-094021/adminexpress-cog-simpl-000-2024.gpkg",
               layer = "commune")

Processing

We will create voronoï polygons from grouped postal codes points.

st_rename_geom <- function(x, name) {
  names(x)[names(x) == attr(x, "sf_column")] <- name
  st_geometry(x) <- name
  return(x)
}

# We need to use a projection for each territory to avoid geometry errors
voronoi <- function(df, k) {
  df_proj <- df |> 
    st_transform(pull(k, proj)) 
  
  df_proj |> 
    st_union() |> 
    st_voronoi() |> 
    st_cast() |> 
    st_intersection(st_transform(fr, pull(k, proj))) |> 
    st_sf() |> 
    st_rename_geom("geom") |> 
    st_join(df_proj) |> 
    group_by(code_postal) |> 
    summarise() |> 
    st_transform("EPSG:4326")
}

# get the names of the main town of each postal code
noms <- cp_points |> 
  st_join(com |> 
            select(insee_com, nom, population)) |> 
  group_by(code_postal) |> 
  slice_max(population, n = 1, with_ties = FALSE) |> 
  select(code_postal, nom) |> 
  st_drop_geometry()

# create the voronoï for each territory
cp_poly <- cp_points |> 
  group_by(proj) |> 
  group_modify(voronoi) |> 
  ungroup() |> 
  select(-proj) |> 
  st_sf() |> 
  left_join(noms, join_by(code_postal))

Map

An extract only on métropole:

cp_poly |> 
  filter(str_sub(code_postal, 1, 2) < "97") |> 
  st_transform("EPSG:2154") |> 
  ggplot() +
  geom_sf(fill = "#eeeeee",
          color = "#bbbbbb", 
          linewidth = .1) +
  labs(title = "Codes postaux",
       subtitle = "France métropolitaine - 2024",
       caption = glue("https://r.iresmi.net/ - {Sys.Date()}
                      data: La Poste")) +
  theme_void() +
  theme(plot.caption = element_text(size = 6, color = "darkgrey"))

Map of french postal codes — Figure 1: France – postal codes 2024

Export

cp_poly |> 
  st_write("codes_postaux_fr_2024.gpkg",
           delete_layer = TRUE,
           quiet = TRUE,
           layer_options = c("IDENTIFIER=Codes postaux France 2024",
                             glue("DESCRIPTION=Métropole + DROM WGS84.
                                  d'après données La Poste + IGN Adminexpress
                                  https://r.iresmi.net/ - {Sys.Date()}")))

Get the file: polygones des codes postaux français 2024 (geopackage WGS84) (3 MB).

Caution

Métropole + DROM (no Polynesia, New caledonia,…)
Some polygons parts (434) cover other polygons in communes where several postal codes are present.
4 NAs (multipolygons without postal codes) are present covering territories outside the voronoï polygons.
No postal code for St-Barth/St-Martin?

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