Comes from the latest Startup Genome report:
"Its startup density is second only to Silicon Valley and a full 50% higher than its closest follower. How can such a small city compete against cities 10 to 30 times their size such as Rio, Atlanta and Rome?"
http://blog.compass.co/waterloo-the-david-vs-goliath-of-star...
Will add the citation to the Medium post as well.