Author: gregory.huang

GeoVis: Mapdeck Package in R

Gregory Huang
Geovisualization Project, @RyersonGeo, Fall 2019

Introduction

This project is a demonstration of the abilities of the mapdeck package in R, including its shiny interactive app compatibility.

Mapdeck is an R package created by David Cooley. Essentially, it integrates some of mapbox’s functionality into the R environment. Mapbox is a popular web-based mapping service that is community-driven and provides some great geovisualization functionalities. Strava’s global heat map is one example.

I am interested in looking at flight routes across global hubs and see if there are destination overlaps for these routes. Since the arc layer provided by mapdeck has impressive visualization capabilities of the flight routes, I’ve chosen to use mapdeck to visualize some flight route data around the world.

Example of a map generated by mapdeck: arcs, text, lines, and scatterplots are all available. Perspective changes can be done by pressing down Ctrl and clicking. The base maps are customizable with a massive selection of both mapbox and user-generated maps. This map is one of the results from longest_flights.R, which uses the “decimal” basemap.
The Map has some level of built-in interactivity: Here is an example of using a “tooltip” where if a user hovers over an arc, the arc highlights and shows information about that particular route. Note that mapdeck doesn’t want to draw flight routes across the Pacific – so if accuracy is key, do keep this in mind.

Software Requirements

To replicate this project, you’ll need your own mapbox access token. It is free as long as you have a valid email address. Since the code is written in R, you’ll also need R and R Studio downloaded on your machine to run the code.

Tl;dr…

Here’s the Shiny App

The code I created and the data I used can also be found on my GitHub repository, Geovis. To run them on your personal machine, simply download the folder and follow the instructions on the README document at the bottom of the repository page.

Screenshot of the shiny app: The slide bar will tell the map which flights to show, based on the longitudes of the destinations. All flights depart out of YYZ/KEF/AMS/FRA/DXB.

Details: Code to Generate a Map

The code I’ve written contained 2 major parts, both utilizing flight route data. The first part is done with longest_flights.R, demonstrating the capabilities of the mapdeck package using data I curated for the longest flights in the world. The second part is done with yyz_fra.R and shinyApp.R to demonstrate the shiny app compatibility and show how the package handles larger datasets (hint – very well). The shinyApp uses flight route data from 5 airports: Toronto, Iceland-Keflavik, Amsterdam, Frankfurt, and Dubai, pulled from openflights.org.

For the flight route data for the 5 airports, in particular, the data needed cleaning to make the data frame useable to mapdeck. This involved removing empty rows, selecting only the relevant data, and merging the tables.

Code snippet for cleaning the data. After the for loop completes, the flight route data downloaded from openflights.org becomes available to be used for mapdeck.

Once the data were cleaned, I began using the mapdeck functions to map out the routes. The basic parts of the mapdeck() function are to first declare your key, give it a style, and assign it a pitch if needed. There are many more parameters you can customize, but I just changed the style and pitch. Once the mapdeck map is created, use the “pipe” notion (%>%) to add any sort of layers to your map. For example, add_arc() to add the arcs seen in this post. Of course, there are many parameters that you can set, but the most important are the first three: Where your data come from, and where the origin/destination x-y coordinates are.

An example creating an arc on a map. In addition to the previously mentioned parameters, tooltip generates the little chat boxes when you hover over a layer entry, and layer_id is important when there are multiple layers on the same map.

Additional details on creating all different types of layers, including heatmaps, can be found on the documentation page HERE.

Details: Code to make a “Shiny” app

On top of the regular interactive functionalities of mapdeck, incorporating a mapdeck map into shiny can add more layers of interactivity to the map. In this particular instance, I added a slider bar in Shiny where the user can indicate the longitudes of the destinations they want to see. For example, I can filter to see just the flights going to East Asia by using that slider bar. Additional functions of shiny include using drop-menus to select specific map layers, and checkboxes as well.

The shiny code can roughly be broken down into three parts: ui, server, and shinyApp(ui, server). The ui handles the user interface and receives data from the server, while the server decides what map to produce by the input given by the user in ui. shinyApp(ui,server) combines the two to generate a shiny app.

Mapdeck integrates into the shiny app environment by mapdeckOutput() in ui to specify the map to display, and by renderMapdeck() and mapdeck_update() in server to generate the map (rendeerMapdeck) and appropriate layers to display (mapdeck_update).

Below is the code used to run the shiny app demonstrated in this blog post. Note the ui and server portions of the code bode. To run the shiny app after that, simply run shinyApp(ui,server) to generate the app.

Creating the UI
Snippet of the Server creation section. Note that the code listens to what the UI says with reactive() and observeEvent().

This concludes my geovis blog post. If you have any questions, please feel free to email me at gregory.huang@ryerson.ca.

Here is the link to my GitHub repository again: https://github.com/greghuang8/Geovis