Welcome to episode 20 of Data Viz Today. What are isochrone maps and how can you use them for advanced analysis or data art? Host Alli Torban dives into specific ways you can create and use isochrones for personal or work challenges. Featured data visualization project by Topi Tjukanov perfectly models how isochrones can bring out interesting insights.
Welcome! I'm Alli Torban.
00:25 - Today’s episode is all about isochrones! What they are and how you can use them for some interesting analysis and beautiful data art. The word isochrone comes from the Greek isos meaning equal and chrono meaning time. Equal time. It’s a line on a diagram or map connecting points relating to the same time or equal times. The useful aspect of isochrones is that the travel times are realistic because it takes into account where the roads are and even traffic conditions.
01:40 - Today’s featured data viz project is called “Urban Forms” by Topi Tjukanov.
02:40 - The first known isochronic map was created by Francis Galton in 1881.
02:50 - So how do you make an isochrone map anyway? Mark your starting point, map out every possible route leaving that point, and then think about your assumptions - how fast are you traveling, and what’s the maximum amount of time that you want to travel. Then for every route, you use the classic formula: distance = rate * time. Solve for distance, and then you can mark a point on the map at the distance you can go when you’re going a certain speed for a certain amount of time. And you repeat that for every possible route. Connect all those points and you have a polygon around your starting point that shows how far you can travel in every direction during that amount of time.
03:30 - As you can imagine, this is really labor intensive, but now there are APIs you can use that can quickly grab all that route and travel distance information for you.
03:40 - When Topi came across the HERE.com API and a python tutorial on how to convert the coordinates to polygons, he decided to try the code out for himself and experiment with what the different isochrone polygons looked like for different cities.
04:15 - The Python scripts that can be run inside the QGIS Python Console.
04:45 - He dropped starting points in 20 different european cities and ran generated 144 isochrones for each city - one for every 10 minutes during a 24 hour period and over-layed all those isochrones on top of each other so that you can get a realistic view of how far you can go in each city in an hour by car no matter what the traffic is like.
06:15 - It’s fun thinking about the transportation infrastructure of the city that’s causing these different shapes, or the natural features like oceans, lakes, mountains that also affect the shape. It’s like a fingerprint for the city.
06:55 - What are some ways you can use isochrones for geospatial analysis?
You can do two isochrones - one around your work and another around your partner’s work and see where they overlap so you can find a home that’s in an area where you both have suitable commutes.
Or you can map out potential store locations within a city and try to minimize the overlap of the isochrones around each location so your store locations cover as much of the city as possible.
What kind of foot traffic can we expect for a store, at this location? What kind of delivery coverage can we offer? Where are our competitor’s delivery holes that we could fill.
How many homes can a firehouse serve within a 10-minute drive?
Where should we put each firehouse so that there’s a firehouse within 5 minutes of every house?
Which workers are within a 15 minute drive of this outage?
How far could this stolen vehicle have gotten by now?
If we put a bus stop there, how many riders will live within a 5-minute walk?
It’s also used to show how long it takes for runoff water within a drainage basin to reach a lake or outlet.
Chris Slatt used an isochrone map to show how much time it took for residents in different parts of a Maryland city to take public transit to jury duty and showed that more than half wouldn’t be able to make it to the courthouse by the time it opens in the morning.
08:40 - How do you generate an isochrone?
09:45 - My inspired viz - I used isochrones for analysis for an article that I wrote for a local magazine to see how much extra it costs to buy a house that’s within a 10 minute walk of a metro station compared to the rest of the city.
10:30 - My final takeaway is that isochrones are a super cool tool for art and analysis - and now there are more and more ways that for everyone to take advantage of them. Take a page out of Topi’s book and experiment with it a little, maybe make some data art with it, and then you’ll know how to do it when it comes time to use it!
11:35 - Get mapping right away with my free-mini course “Make Your First Custom Map in Under 30 Minutes”.