Leaflet for mapping

Maps are an important way of displaying data.
The leaflet package in R provides access to the Leaflet Javascript libraries (http://leafletjs.com), an open-source mechanism to create interactive maps. The leaflet package (https://rstudio.github.io/leaflet/) provides an interface within R that allows for composing maps using map tiles (e.g., from OpenStreetMap, https://www.openstreetmap.org/#map=5/38.007/-95.844) that can be annotated with markers, lines, popups.

Here’s a simple example where data from higher education institutions from within the Five College Consortium in Western Massachusetts is mapped.

There are four steps:

1. Create the dataset that will be displayed
2. Create a map widget (according to Wikipedia, a component of an interface that enables a user to perform a function): here we call this m
3. Add layers and tiles
4. Print the map widget to see the results

# step 1: create the dataset
institution <- c("Amherst College", "Hampshire College", "Mount Holyoke College",
                 "Smith College", "University of Massachusetts")
lat <- c(42.3709, 42.325079, 42.255586, 42.318119, 42.3912)
lng <- c(-72.5170, -72.530837, -72.574503, -72.638139, -72.5267)
students <- c(1792, 1175, 2255, 2600, 28635)
label <- paste0("<b>", institution, "</b><br>", students, " students", sep="")
ds <- dplyr::tibble(institution, lat, lng, students, label)
dplyr::glimpse(ds)
## Rows: 5
## Columns: 5
## $ institution <chr> "Amherst College", "Hampshire College", "Mount Holyoke ...
## $ lat         <dbl> 42.37090, 42.32508, 42.25559, 42.31812, 42.39120
## $ lng         <dbl> -72.51700, -72.53084, -72.57450, -72.63814, -72.52670
## $ students    <dbl> 1792, 1175, 2255, 2600, 28635
## $ label       <chr> "<b>Amherst College</b><br>1792 students", "<b>Hampshir...

Here we have used simple html markup to create a two line label, with institution bolded, that will be displayed.

# steps 2-3: generate leaflet map 
library(leaflet)
m <- leaflet(ds) %>% 
  addTiles() %>% 
  addMarkers(~lng, ~lat, popup = ~ label)
m # step 4: display the results

The popups for each of the five institutions can be clicked to see information contained in the label variable. Here’s an example of what happens if Amherst College is clicked: