Interactive maps in html

Maps are invaluable for environmental data, but sometimes it seems overwhelming to interact with GIS system or other mapping environment (google earth, anyone?)

leaflet

leaflet builds html maps with interactive features.

There is an R implementation, though leaflet itself is a commonly used JavaScript library with many native extensions.

Install and load library

install.packages('leaflet')
library(leaflet)

basic functionality: leaflet()

The leaflet mapping interface works in layers, like ggplot, but with the ‘pipe’ operator, like dplyr:

p <- leaflet() %>% 	# call function, can be empty
  addTiles() %>% 	# add basemap, default is open street maps
  setView(lat = 44.963, lng = -93.22, zoom = 14) # options

Examine resulting map object, noting:

• opens in Viewer, not in Plot window (html code)
• pans and zooms like regular web map
• can open in browser, save, etc

plot data on top of nice basemap

# some lat-long data incl translated from DMS
lats <- c(44.974747, (44 + 58/60 + 23/3600), 44.9848671)
lons <- c(-93.235353, -(93 + 14/60 + 40/3600), -93.1824609 ) 

p <- leaflet() %>% 
  addTiles() %>% 
  addMarkers(lng = lons, lat = lats, popup = c('EB', 'WB', 'StP'))

Examine resulting map object noting:

• automatic zoom to extent of data
• interactive labels on click

Do Exercise 4: Add leaflet to markdown