John Snow and 1854 cholera epidemic

The Broad Street pump

Outright lies

Fake maps and junk maps

Points can be useless

Choropleths can be great

Choropleths can distort

Land doesn't vote

Cartograms

Projections

Animated world projections

World projections

US projections

Finding projection codes

spatialreference.org

epsg.io

proj.org

Most common ones listed on the
course website example page

This is an excellent overview of how this all works

And this is a really really helpful overview of all these moving parts

Which projection is best?

None of them

There are no good or bad projections

There are appropriate and
inappropriate projections

(but also ew mercator)

Maps with lines

Maps with lines

Maps with points

Maps with points

Maps with points

Voronoi maps

Maps with shapes

Small multiples that look like maps

Shapefiles

Geographic information is shared as shapefiles

These are not like regular single CSV files!

Shapefiles come as zipped files with
a bunch of different files inside

Structure of a shapefile

library(sf)
world_shapes <- read_sf("data/ne_110m_admin_0_countries/ne_110m_admin_0_countries.shp")

## Simple feature collection with 7 features and 3 fields
## Geometry type: MULTIPOLYGON
## Dimension:     XY
## Bounding box:  xmin: -180 ymin: -18 xmax: 180 ymax: 83
## Geodetic CRS:  WGS 84
## # A tibble: 7 × 4
##   TYPE              GEOUNIT                  ISO_A3                               geometry
##   <chr>             <chr>                    <chr>                      <MULTIPOLYGON [°]>
## 1 Sovereign country Fiji                     FJI    (((180 -16, 180 -17, 179 -17, 179 -17…
## 2 Sovereign country Tanzania                 TZA    (((34 -0.95, 34 -1.1, 38 -3.1, 38 -3.…
## 3 Indeterminate     Western Sahara           ESH    (((-8.7 28, -8.7 28, -8.7 27, -8.7 26…
## 4 Sovereign country Canada                   CAN    (((-123 49, -123 49, -125 50, -126 50…
## 5 Country           United States of America USA    (((-123 49, -120 49, -117 49, -116 49…
## 6 Sovereign country Kazakhstan               KAZ    (((87 49, 87 49, 86 48, 86 47, 85 47,…
## 7 Sovereign country Uzbekistan               UZB    (((56 41, 56 45, 59 46, 59 46, 60 45,…

Where to find shapefiles

Natural Earth for international maps

US Census Bureau for US maps

For anything else…

Scales

1:10m = 1:10,000,000

1 cm = 100 km

1:50m = 1:50,000,000

1cm = 500 km

1:110m = 1:110,000,000

1 cm = 1,100 km

Using too high of a resolution
makes your maps slow and huge

Latitude and longitude

The magic geometry column

As long as you have a magic geometry column,
all you need to do to plot maps is geom_sf()

ggplot() +
  geom_sf(data = world_shapes)

The magic geometry column

Use coord_sf() to change projections

ggplot() +
  geom_sf(data = world_shapes) +
  coord_sf(crs = "+proj=merc")

The magic geometry column

Use coord_sf() to change projections

ggplot() +
  geom_sf(data = world_shapes) +
  coord_sf(crs = "+proj=robin")

Use aesthetics like normal

All regular ggplot layers and aesthetics work

ggplot() +
  geom_sf(data = world_shapes, 
          aes(fill = POP_EST),
          color = "white", size = 0.15) +
  coord_sf(crs = "+proj=robin") +
  scale_fill_gradient(labels = scales::comma) +
  labs(fill = NULL) +
  theme_void() +
  theme(legend.position = "bottom")

No geometry column?

Make your own with st_as_sf()

other_data

## # A tibble: 2 × 3
##   city            long   lat
##   <chr>          <dbl> <dbl>
## 1 Atlanta        -84.4  33.8
## 2 Washington, DC -77.1  38.9

other_data %>% 
  st_as_sf(coords = c("long", "lat"), 
           crs = st_crs("EPSG:4326"))

## Simple feature collection with 2 features and 1 field
## Geometry type: POINT
## Dimension:     XY
## Bounding box:  xmin: -84 ymin: 34 xmax: -77 ymax: 39
## Geodetic CRS:  WGS 84
## # A tibble: 2 × 2
##   city              geometry
## * <chr>          <POINT [°]>
## 1 Atlanta           (-84 34)
## 2 Washington, DC    (-77 39)

sf is for all GIS stuff

Draw maps

Calculate distances between points

Count observations in a given area

Anything else related to geography!

See here or here for full textbooks

geom_sf() is today’s standard

You'll sometimes find older tutorials and StackOverflow answers about using geom_map() or ggmap or other things

Those still work, but they don't use the same magical sf system with easy-to-convert projections and other GIS stuff

Stick with sf and geom_sf()
and your life will be easy