PPOL 6805 / DSAN 6750: GIS for Spatial Data Science
Fall 2025
Tuesday, September 17, 2024
“Simplest” / Most Efficient Representation
“Indicate which of the seven geometries above would provide the simplest representation of the entity”
GEOMETRYCOLLECTION
could represent any of the geographic entities in Q1, but would be overkill for representing e.g. a single point or line
For the United Arab Emirates (UAE) data… we have what we call the Not-Paraguay-Problem: Most countries, including the UAE, have a bunch of lil “pieces”:
So, for Q1.8: Assume we’re just trying to have the computer represent the “mainland” (the biggest contiguous landmass, with Dubai on it!)
From Krygier and Wood (2016)
The Earth’s “width” is slightly greater than its “length” 😰
From Wikimedia Commons
From Monmonier (2018)
Kieran Healy, “America’s Ur-Choropleths”
Kieran Healy, “America’s Ur-Choropleths”
From Reddit
From Wikimedia Commons
From Monmonier (2018)
From Monmonier (2018)
Is poverty a “significant issue” in the US?
From Krygier and Wood (2016)
Is poverty a “significant issue” in the US?
Assigns the same number of observations to each color
From Krygier and Wood (2016)
Is poverty a “significant issue” in the US?
Boundaries between colors come at regular (equal) intervals
From Krygier and Wood (2016)
Is poverty a “significant issue” in the US?
Clustering algorithm chooses classes to (a) minimize differences within classes, (b) maximize differences between classes
From Krygier and Wood (2016)
Is poverty a “significant issue” in the US?
A government program offers special funding for counties with above 25% poverty
From Krygier and Wood (2016)
Is poverty a “significant issue” in the US?
From Krygier and Wood (2016)
Using rnaturalearth
with mapview
Computing the union of all geometries in the sf
via sf::st_union()
library(leaflet.extras2)
africa_sf <- ne_countries(continent = "Africa", scale = 50)
africa_union_sf <- sf::st_union(africa_sf)
africa_map <- mapview(africa_sf, label="geounit", legend=FALSE)
africa_union_map <- mapview(africa_union_sf, label="st_union(africa)", legend=FALSE)
africa_map | africa_union_map
Use st_union()
first:
Computing the centroid of all geometries in the sf
via sf::st_centroid()
PPOL 6805 Week 4: Unary and Binary Operations