I just released Mapnificent for 17 cities in the US and some other cities world wide (before Mapnificent was only available for Berlin and somehow for London night buses). You can watch a short video about what Mapnificent is and what it can do here. This post will explain how Mapnificent works and how I scaled it up to more than 20 cities with hopefully more cities to come.
From the GTFS data Mapnificent knows all routes and their stops, how long a route needs between two stops and the average headway of each route in a given time range (e.g. in the morning). This is compressed into JSON and delivered to your browser. When you set a point, Mapnificent looks for the closest couple of stations, then starts to travel to every station in the network it can reach and records the minimum amount of time it takes to a station. The calculation process runs in a Web Worker thread. For some smaller public transport systems it is so fast that I can enable the “Calculate on Drag” feature: check it out for Sacramento and Berlin.
There is a major heuristic involved: how can Mapnificent know how long a trip takes when it doesn’t even know the exact time the next bus/train/helicopter departs from a stop? It really can’t know for sure. To compensate for this lack of knowledge Mapnificent makes some assumptions.
It assumes that you will time your journey in a way that you don’t have to wait for your first transport option. Of course this does not always hold in real life, but it’s a reasonable assumption to work with.
It assumes further that if you change transportation, you will probably not immediatley catch the next bus/train/spaceship. The average waiting time could be thought of as headway divided by two. However, I found that the waiting time (for Berlin) is actually lower. That can be explained by the fact that the public transport agency supposedly designed the timetables in a smart way that allows connecting trains/busses/submarines to wait for each other in order to let riders change more quickly. Also people plan their trips in a way that reduces waiting time. So the waiting time can be considered to be less than the mathematical average. I tried around a bit with a logarithmic formula which worked ok for Berlin, but for the whole world I settled for a simpler approach: headway divided by three.
How accurate is it?
Difficult to say. I have actually never been to any of the cities except Berlin and London, so I don’t know if any important transportation options are missing (because they are not available as a GTFS feed) or if anything is totally incorrect. I created Mapnificent for Berlin first (because I usually live there) and then used it as the basis for a seminar at Hasso Plattner Institute (where I’m a Master student). There I actually had the chance to compare the times calculated by Mapnificent Berlin (starting point was Berlin main station) to times from an actual trip planner command line interface. Here is a graph that shows how many errors in minutes there were for trips to every station in Berlin:
You can see that the majority of trips (53 %) have an error less than or equal to 5 minutes and 96 % have an error of less than or equal to 20 minutes. I traced the outliers to stops only reachable by very infrequent buses with headways of around an hour. This gave me some confidence about the relative accuracy of Berlin, but at the moment I can’t do the same analysis for all the other cities I added to Mapnificent. I asked friends to check out some routes in cities they know and it seemed to be sufficiently correct to them. If you find anything totally odd, please contact me.
Mapnificent requires Web Worker and Canvas to work. I tried the latest official versions of Opera (fast), Chrome (fast), Safari (ok) and Firefox (slow) as well as the latest beta versions of Webkit, Chromium (both seem to have a bug that cuts of the lower part of the canvas) and Firefox 4. I didn’t try Internet Explorer 9 (not sure if they already have Web Worker support), but I don’t have Vista or Windows 7, so I won’t be able to test it there anyways.
If I was a research department in a big company I would say that the product is ready for the browsers of the average web user in 2-3 years and would wait accordingly. But since that is not the case, I release it now, even though it pains me to see people using Mapnificent in suboptimal environments. Please browser developers, make that pain go away soon.
What is it for?
Mapnificent ist not a trip planning service and you should in fact use the trip planning services of the public transport providers that are linked to in the bottom left corner of the site.
The old Mapnificent
I ported Berlin and London to the new Mapnificent, but they both rely on hand scraped data sources which are difficult to maintain. The old blog post about Mapnificent is wildly outdated, but might be fun read. The source of the new Mapnificent is not published as Open Source at the moment (I still have to sort some stuff out), but you can still find the old Mapnificent source on my GitHub account.
I want to thank all the beta testers that gave awesome feedback, Mapnificent would be uglier and less usable without you. I am excited to bring this project to the next level and I can’t even begin to imagine where Mapnificent is going from here.
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