Indeed. Each company requires user input and manual validation. The selection bias is self evident.
Yeah, the data set is really, really incomplete -- it only includes 7 startups in the Bay Area, for example. Plus, the UI is such that even if the data set were more complete, it would be hard to get a true sense of the density of startups in certain areas.
I would definitely have ranked Boston MA, approximately between Roma and Salerno (Italy), on the startup hub list.