The east-west divide We're picking up speed, but not at the same pace. On the maps below, blue means fast and red means slow, when compared with the city-wide median finishing time across 15 years of minutes and 42 seconds. (This means half the participants ran faster than this time and the other half ran slower.)

"Poorer people have poorer health outcomes and western Sydney is traditionally lower SES [socioeconomic status]," says University of Sydney researcher Jennifer Kent, an expert in how urban design influences health. Worse access to public transport, longer commutes and more time driving mean people in the west have less time to exercise or buy and cook healthy food, she says. The west also has fewer green open spaces than the east.

This is a clear warning that a section of the population is being left behind, Dr Kent says. "We have all these opportunities to engage in healthy behaviour in inner, urban areas but there's this rift we're creating, this huge divide, between the 'haves' and the 'have-nots'." Women are catching up to men Men, watch your backs. Women have improved five times faster than men over the past 15 years, cutting roughly 16 per cent from their finishing times since 2000, compared with 3 per cent for men.

That's a 22-minute gain for women, compared with 2.5 minutes for men. This dwindling gender gap, also seen among elite athletes, comes down to two factors that have the same effect: growing the pool from which participants are drawn. "The population overall is increasing and the run is getting more and more popular. That's why times are getting better," says public health expert Timothy Olds, from the University of South Australia's Sansom Institute for Health research. "The bigger the population the more likely you are to get people at the extremes, the really good performers."

This effect can be seen in the charts, below, which track the evolution of the "typical" male and female runner. The charts show the distribution of participants by finishing time. The dual bumps in each chart represent the two main groups: runners (on the left) and walkers (on the right). The shape of the women's chart has become much more similar to the men's over 15 years. In the early 2000s, female walkers outnumbered runners. But by 2011-15 women were roughly 1.5 times more likely to run than to walk. Rising gender equality means female participation rates have grown far more rapidly than men's, Professor Olds says. (Even in 1971, only 2 per cent of runners in the first City2Surf were women, compared with 51 per cent in 2015.)

"And that's obviously influenced by social and cultural issues" that have historically discouraged women from playing sport, he says. "It wasn't considered very ladylike." We're all getting faster Both the men's and women's charts show the number of runners and the number of participants have risen hand-in-hand. This means the whole city is running faster. In the early 2000s our "fastest" postcodes were finishing in roughly 95 minutes; our "slowest" in 2 hours and 53 minutes. By 2011-15, the fastest were finishing in under 85 minutes; the slowest in around 2 hours and 10 minutes.

At the same time, the gap between our fastest and slowest postcodes has shrunk from 24 minutes in 2000-04 to 18 minutes in 2011-15. "The average punter is now better prepared … There's better support, focus training groups, more people are educated in how to train," UTS sport and exercise scientist Aaron Coutts says. "It's almost like a high performance mindset, where the challenge used to be to walk [the race] but now, people aim to run it." It's a bright spot in an era of soaring obesity rates and declining physical activity, Professor Coutts says. Loading