Toronto's centre trumps the suburbs in the numbers of commuter and utilitarian cyclists, but that doesn't mean there aren't still a lot of cyclists all over the city. The difference, however, between centre and suburbs is that cyclists in the suburbs are spread thinly over an area five times as big as the central urban area.
In this map I've divided Toronto into two regions: urban centre and suburban. This division is mostly based on population density with the dense urban centre bounded by Keele to Woodbine and St. Clair, and the less dense suburbs everything outside of that.
Working with two sources I was able to get some reasonable - though rough - numbers on the centre/suburb split of utilitarian cyclists (those who use the bike for work, school, errands, shopping or visiting) and commuter cyclists (those who use bikes as their primary commuter mode). Commuter cyclists are really also utilitarian cyclists so my map assumes the Census commuter cyclists to be a sub-set of the Decima utilitarian cyclists (though this is a bit of cheating since the data was collected quite differently).
The utilitarian cycling numbers are from the 1999 Decima survey by the City of Toronto (I hear they are finally doing another one 10 years later). And the commuter cycling numbers are from the Census 2001 of the Toronto Census Division (bounded by the actual City of Toronto) 1.15 million people (46% of population) commuted to work. Approximately 45,000 people commuted to work by bicycle as their primary mode of transportation.
The centre is heavily weighted for commuter cyclists with 71% (32,000) in the urban centre to the suburbs' 29% (13,000). Urban utilitarian cyclists make up 58% (280,500) of all utilitarian cyclists with 42% (206,465) in the suburbs.
Anyone who cycles in the suburbs, however, will quickly realize that utilitarian cyclists are still spread very thinly. In the suburbs I find that I feel like waving or staring at every cyclist that's actually on the road - we're like comrades. In downtown Toronto other cyclists are background noise. Since the suburbs take up about 5 times the area (288 square km to 55 square km) and are much less dense than the centre (about 6000 persons per square kilometre in the suburbs compared to 17,000 persons per square kilometre in the centre), this means that the suburban utilitarian cyclists are spread out. The centre has about 550 commuter cyclists per square kilometre compared to about 50 commuter cyclists per square kilometre in the suburbs. There are 5100 utilitarian cyclists per square kilometre in central Toronto, and 720 utilitarian cyclists per square kilometre in the suburbs)
We must bracket the commuter cycling numbers. They only measure the people who were asked at home if they commuted to work and used bicycles as their primary mode. It leaves out people who use bikes as a secondary mode, and it doesn't measure people who use bikes for other purposes, including running errands or for business. For that the City's utilitarian cyclist numbers give a more complete picture. The overall trend is the same, however: there are just more utilitarian cyclists per square kilometre in downtown than the burbs.
My last map showed the location of bike union members. According to my quick and dirty calculations it looks like about 15% of all bike union members were outside of the centre. When suburban memberships rise to 30-40% we could safely say that they are no longer under-represented. Despite my earlier claims to the contrary, I think the bike union needs to do more work in the suburbs to be truly representative. They'll have to cover a lot of sparse territory but needed.