You've got 30 minutes and a bus pass. The world is your weirdly shaped blob.
These blobs represent the extent that you'd be able to travel on public transit in 30 minutes. The 20 maps below were made by Mapnificent, a new website created by Stefan Wehrmeyer that suck in Google Maps-friendly transit data to show just how much of the city you can cover in however much time you want to spend. A handy slider allows you to change your allotted time, and your starting point can be anywhere on the map.
As these maps reveal, 30 minutes on public transit can take you a surprisingly long way in some cities, and keep you severely contained in others. Miami, for example, offers a pretty tight window on the world, compared with transit-rich cities like London and New York.
Wehrmeyer notes that not every city's data sets are fully available, so some maps aren't exact. They calculate time from the starting point assuming that your bus or train leaves on time – a farcical concept in some places. They do however account for time waiting between transfers, which gives them a dose of reality.
All these maps were captured at roughly the same scale to offer comparisons between places. U.S. cities are shown first, followed by Canadian cities, then by European cities. Each region's cities are shown in order of descending population.
So if you ever find yourself with a bus token and a half hour in any of these cities, you'll know you've got some options.