Figure 4.5 Te Reo Māori toponyms in Aotearoa

figures

code

I made an alternative version of this map for some slides. It shows off the little-known multiplication by an affine transform matrix superpower that sf somewhat surprisingly admits (it felt like a cheat-code when I came across it here).

Code

library(sf)
library(ggplot2)
library(dplyr)

Here’s the superpower in action where we make an affine rotation matrix and multiply the geometries in the dataset by it. You can use similar operations to translate geometries, although keeping everything lined up can be tricky.

Code

ang <- 40 * pi / 180
rotation <- matrix(c(cos(ang), -sin(ang), 
                     sin(ang),  cos(ang)), 2, 2, byrow = TRUE)

nz <- st_read("nz-2193.gpkg") |>
  st_cast("POLYGON") |>
  mutate(geom = geom * rotation)

Reading layer `nz-2193' from data source 
  `/Users/david/Documents/code/computing-geographically/chapters/chap4/nz-2193.gpkg' 
  using driver `GPKG'
Simple feature collection with 1 feature and 0 fields
Geometry type: MULTIPOLYGON
Dimension:     XY
Bounding box:  xmin: 1089973 ymin: 4748123 xmax: 2089535 ymax: 6194308
Projected CRS: NZGD2000 / New Zealand Transverse Mercator 2000

Code

toponyms <- st_read("placenames.gpkg") |>
  mutate(maori = reo > 0) |>
  mutate(geom = geom * rotation) |>
st_filter(nz)

Reading layer `placenames' from data source 
  `/Users/david/Documents/code/computing-geographically/chapters/chap4/placenames.gpkg' 
  using driver `GPKG'
Simple feature collection with 47417 features and 9 fields
Geometry type: POINT
Dimension:     XY
Bounding box:  xmin: 502051.1 ymin: 4460560 xmax: 2239532 ymax: 6638458
Projected CRS: NZGD2000 / New Zealand Transverse Mercator 2000

And now a map with colour choices in large measure dictated by the slides I was making this map for.

Code

ggplot() +
  geom_sf(data = nz, fill = "#eee8d5") +
  geom_sf(data = toponyms |> arrange(id), aes(colour = maori), size = 0.01, alpha = 0.2) +
  scale_colour_manual(values = c("slategrey", "red")) +
  guides(colour = "none") +
  theme_void() +
  theme(panel.background = element_rect(fill = "#002b36"))

As noted in the book, the materials for this figure draw on the amazing work of Chris McDowall and Tim Denee in their We Are Here atlas, the Toitū Te Whenua – Land Information New Zealand gazetteer of placenames, and on Te Hiku Media’s Ngā-kupu tools.

Code

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