08-parks-tessellation-green.R

library(dplyr)
library(ggplot2)
library(osmdata)
library(sf)
library(purrr)
library(cowplot)

library(spatstat)
library(maptools)

theme_set(theme_minimal())

# Christchurch limits
chch <- st_read('./data/chchshape/Christchurch_TA.shp')

# Read green areass data from Openstreetmap
greens <- opq(bbox = 'christchurch, new zealand') %>% 
  add_osm_feature(key = 'leisure', value = 'park') %>% 
  osmdata_sf()

# Polygons to Spatial format (for part A)
parks_poly <- greens$osm_polygons %>% 
  st_transform(2193)

parks_inside <- parks_poly[chch,]

part_a <- ggplot() + geom_sf(data = parks_inside, fill = 'chartreuse4') +
  geom_sf(data = chch, alpha = 0, colour = 'black') +
  coord_sf(xlim = c(1550000, 1581950), ylim = c(5165606, 5194534))

parks_inside <- as_Spatial(parks_inside)
part_a <- tm_shape(parks_inside) + tm_polygons('chartreuse4') + 
  tm_shape(chch, bbox = tmaptools::bb(c(1554369, 1581950, 5165606, 5194534), 2, 2)) +
  tm_borders('black')
  
# Extracting park polygons' centroids (to start part B)
parks <- greens$osm_polygons %>% 
  st_transform(2193) %>% 
  select(osm_id) %>% 
  mutate(area = as.numeric(st_area(.))) %>% 
  st_set_geometry(value = st_centroid(st_geometry(.))) %>% 
  mutate(x = map_dbl(geometry, 1),
         y = map_dbl(geometry, 2))

# Tesselation loosely based on https://mgimond.github.io/Spatial/interpolation-in-r.html
parks_ng <- as_Spatial(parks[chch,])
parks_ng@bbox <- as_Spatial(chch)@bbox

tess2 <- as(dirichlet(as.ppp(parks_ng)), 'SpatialPolygons')
proj4string(tess2) <- proj4string(parks_ng)
parks_tess2 <- over(tess2, parks_ng)
parks_tess2_df <- SpatialPolygonsDataFrame(tess2, parks_tess2)
parks_tess2_clipped <- raster::intersect(as_Spatial(chch), parks_tess2_df)

part_b <- ggplot() + 
  geom_sf(data = st_as_sf(parks_tess2_clipped), aes(fill = log10(area))) +
  coord_sf(xlim = c(1550000, 1581950), ylim = c(5165606, 5194534)) +
  scale_fill_gradient(low = '#b2e2e2', high = '#006d2c') +
  theme(legend.position="none")
  
plot_grid(part_a, part_b)
ggsave('./outputs/08-parks-voronoid-green.png')