The giant French Olympic-size swimming pool

Day 7 of 30DayMapChallenge : « Openstreetmap » (previously).

What if all private swimming pools could be merged into one 25 m width pool? OSM is not just a map, it’s a database, so ask OSM… I know that not all swimming pools are present in OSM, but it’s just an exercise and it can give us an order of magnitude or at least a minimum.

We will use a simplified map of France in the background and ask to the Overpass API (with {osmdata}) all « leisure=swimming_pool » and « access=private ». It takes 6 hours and 15 Go of RAM…

library(dplyr)
library(readr)
library(ggplot2)
library(sf)
library(osmdata)
library(ggspatial)
library(glue)
library(httr)
library(units)

fr_bbox <- getbb("France métropolitaine", featuretype = "area")

GET("http://r.iresmi.net/wp-content/uploads/2021/12/adminexpress_simpl.gpkg_.zip",
    write_disk("~/adminexpress_simpl.gpkg_.zip"))
dir.create("~/adminexpress")
unzip("~/adminexpress_simpl.gpkg_.zip", exdir = "~/adminexpress")

fr <- read_sf("~/adminexpress/adminexpress_simpl.gpkg", layer = "region") %>% 
  filter(insee_reg > "06")

# 6 hours
pool <- opq(fr_bbox, timeout = 600) %>%
  add_osm_feature(key = "leisure", value = "swimming_pool") %>% 
  add_osm_feature(key = "access", value = "private") %>% 
  osmdata_sf()

pool_p <- pool$osm_polygons %>% 
  select(osm_id)
pool_mp <- pool$osm_multipolygons %>% 
  select(osm_id)

rm(pool) ; gc()

pool_fr <- pool_p %>% 
	st_filter(fr) %>% 
	mutate(area = st_area(geometry)) %>% 
  bind_rows(pool_mp %>% 
              st_make_valid() %>% 
              st_filter(fr) %>% 
              mutate(area = st_area(geometry)))

olympic_pool_dim <- pool_fr %>% 
	st_drop_geometry() %>% 
	summarise(total_area = drop_units(sum(area, na.rm = TRUE))) %>% 
  mutate(width = 25,
         length = total_area / width)

# centroid_fr <- fr %>% 
#   st_transform("EPSG:2154") %>% 
#   st_union() %>% 
#   st_centroid()

rot <- function(a) matrix(c(cos(a), sin(a), -sin(a), cos(a)), 2, 2)

olympic_pool <- c(0, 0,
                  0, olympic_pool_dim$length, 
                  olympic_pool_dim$width, olympic_pool_dim$length,
                  olympic_pool_dim$width, 0,
                  0, 0) %>% 
  matrix(ncol = 2, byrow = TRUE) %>% 
  list() %>% 
  st_polygon() %>% 
  st_sfc(crs = "EPSG:2154") *
  rot(pi / 4) + 
  c(400000, 6300000)

fr %>% 
  st_transform("EPSG:2154") %>% 
  ggplot() +
  geom_sf() +
  geom_sf(data = st_sf(olympic_pool, crs = "EPSG:2154"), color = "blue") +
  labs(title = "The giant French Olympic-size swimming pool",
  	   subtitle = glue("What if all private swimming pools could be merged
                        into one 25 m width pool?"),
       caption = glue("pool data from © OpenStreetMap contributors
                      map IGN Adminexpress
                      r.iresmi.net - {Sys.Date()}")) +
  annotation_scale(height = unit(0.1, "cm")) +
  theme_minimal() +
  theme(panel.grid = element_blank(),
        axis.text = element_blank())

ggsave("pool.png", width = 20, height = 12.36, units = "cm", scale = 1.1)

We get an Olympic swimming pool (25 m width) measuring at least 755 km in length !