5.4 Centroids

Centroid operations identify the center of geographic objects.

Analogous to mean/median/mode, there are different ways to calculate centroids (chapter 11)

nz |>
  ggplot() +
  geom_sf() +
  labs(title = "New Zealand",
       subtitle = "where R was born!",
       caption = "GeoComputation with R book club") +
  theme_minimal()

head(nz) #New Zealand

## Simple feature collection with 6 features and 6 fields
## Geometry type: MULTIPOLYGON
## Dimension:     XY
## Bounding box:  xmin: 1568217 ymin: 5518431 xmax: 2089533 ymax: 6191874
## Projected CRS: NZGD2000 / New Zealand Transverse Mercator 2000
##            Name Island Land_area Population Median_income Sex_ratio
## 1     Northland  North 12500.561     175500         23400 0.9424532
## 2      Auckland  North  4941.573    1657200         29600 0.9442858
## 3       Waikato  North 23900.036     460100         27900 0.9520500
## 4 Bay of Plenty  North 12071.145     299900         26200 0.9280391
## 5      Gisborne  North  8385.827      48500         24400 0.9349734
## 6   Hawke's Bay  North 14137.524     164000         26100 0.9238375
##                             geom
## 1 MULTIPOLYGON (((1745493 600...
## 2 MULTIPOLYGON (((1803822 590...
## 3 MULTIPOLYGON (((1860345 585...
## 4 MULTIPOLYGON (((2049387 583...
## 5 MULTIPOLYGON (((2024489 567...
## 6 MULTIPOLYGON (((2024489 567...

nz_centroid = st_centroid(nz)

## Warning: st_centroid assumes attributes are constant over geometries

nz |>
  ggplot() +
  geom_sf() +
  geom_sf(color = "red", data = nz_centroid) +
  labs(title = "New Zealand",
       subtitle = "centroids",
       caption = "GeoComputation with R book club") +
  theme_minimal()

nz |>
  ggplot() +
  geom_sf() +
  geom_sf_label(data = nz_centroid,
                aes(label = Name)) +
  labs(title = "New Zealand",
       subtitle = "labels",
       caption = "GeoComputation with R book club") +
  theme_minimal()