Make maps with Rstats

April 14, 2020 - 2 minutes
Three simple steps to go from open data set to interactive map with sf, dplyr, and leaflet.
Open Data Maps

Making maps

Maps are cool and maps are useful, but I always here people say that making maps is hard. I think making maps is simpler today than ever before. So to show you what I mean, this post is how to map an open spatial dataset.

Get it

Geojson formatted data is available in your local data portal, I promise.

I’m using Census tract data hosted on Charlottesville’s OpenData portal.

## Linking to GEOS 3.7.2, GDAL 2.4.2, PROJ 5.2.0
tracts <- read_sf("")

Wrangle it

This step is the most variable depending on what you have to do. But this data set comes formatted pretty well, so I don’t really have to do much.

I set up a numeric column with the fraction of residents who are black for my fill scale and a character column with text for a tooltip.

## Attaching package: 'dplyr'
## The following objects are masked from 'package:stats':
##     filter, lag
## The following objects are masked from 'package:base':
##     intersect, setdiff, setequal, union
tracts <- tracts %>% 
  mutate(frac_black = round(Black / Population, 2),
         tooltip_text = glue::glue("{frac_black * 100} % of residents are black"))

Map it

Leaflet has been around forever and is used everywhere on the web. There are lots of new mapping packages coming out for R, but I always go back to Leaflet becasue I think the easiest to use.

Leaflet requires scales be defined indendependly so I create a scale to fill with first. Then I pass in column names to polygon arguments, with the ~ syntax, which is very simlar to the aes syntax of ggplot2.


black_pal <- colorNumeric("Greys", tracts$frac_black)

leaflet(tracts) %>% 
  addPolygons(fillColor = ~black_pal(frac_black),
              label = ~tooltip_text,
              color = "black", fillOpacity = 1) %>% 
  addLegend(pal = black_pal, values = ~frac_black,
            title = "Proportion black (2010):",
            opacity = 1) %>% 
  widgetframe::frameWidget(height = '400') # to fix blog CSS conflicts; you probably don't need this line

Wrap up

Maps are super powerful for sharing info about communities. I hope after reading this you feel like you can make a map with Rstats. And I hope you use it visualize some data about where you live.