The analysis is silly. By either by car or public transport, it can easily take 45 minutes to travel from Cambridge, MA to Jamaica Plain, MA, even though they are only one mile apart. This is even more pronounced in NYC. In the urban sprawl that is the Midwest, 15 miles can easily be traversed in 45 minutes.

The analysis would have more bite if it were redone with an eye towards mapping 'temporal' density, rather than spatial density. This would better reflect the ease of meeting in person.