February 2012 GO Transit Zone Map

GO Transit has a fairly opaque pricing scheme. Although the system is based on fare zones, they never tell you how the fare zones work. When you pay, do you pay according to the number of zones that you pass through? Or do you pay by distance between the zones? If you have a monthly pass between two locations, do you also get free travel on GO within those zones that are between those two locations? What happens if there are two routes between two locations, possibly using different zones? Maybe your fare pays for travel in one central zone plus all nearby zones up to a certain distance? Can you tack on an additional zone onto your travel at lower cost?

Fare zone systems can get pretty complicated, so I understand that, for normal people, GO only provides a little online web page where they can enter a source and destination and have GO spit out a total fare. But for the curious, how does the system actually work? For individual bus stops, GO does tell you their fare zone, but I couldn't find a map of all the fare zones on the GO web page. Apparently, even in the GO Transit bylaws discussing the cost of travel, it simply lists a bunch of destinations and then lists the fares for travelling between different pairs of destinations.

So, in an effort to get some insight into how the GO fare zone system worked, I decided to generate a fare zone map for GO. First, I went to the GO website and downloaded the list of stations, their GPS coordinates, and  their fare zones. Then, I put them into the data into a Voronoi diagram generator with the latitude and longitude simply used directly as x and y coordinates. I used Shane O'Sullivan's rewrite of Steven Fortune's original Voronoi code--I needed extra precision though, so I had to use a search and replace to change all the "float"s to "double"s. From there, I took the Voronoi diagram, did a Mercator projection, generated an SVG diagram, overlayed it on an OpenStreetMap map, and I was done.

Data, imagery and map information provided by MapQuest,
Open Street Map and contributors, CC-BY-SA.

My use of Voronoi to generate the diagram obviously has some problems. GO does not provide ferry service, so the zones do not actually extend into Lake Ontario like the diagram shows. There might be zones missing because there are no stops there. Zone 60 ended up being split into two parts because there wasn't a station between Richmond Hill and Vaughan to force the zone to merge together.

Unfortunately, the fare zone map didn't provide me much additional insight into how the fare zone system of GO might work. The zones seem to be irregularly sized, so I think that maybe the GO fare zone system may be more ad hoc with no particular attempt made to let riders buy arbitrary travel in certain zones (i.e. it's optimized for a commuter travel pattern where a commuter always takes the same journey between two locations every day). Oh well.