Southwest Airlines has had a "customer of size policy" for more than 20 years, requiring passengers to buy a second seat on a full plane if their body crosses the armrest boundary.

CNN: Airline policies juggle larger passengers

Even measuring the boundary of a static body of water is no mean feat.

ECONOMIST: Beno?t Mandelbrot

With the ball set to fly for six, long-on fielder Voges made the catch on the boundary, but his body's momentum took him over the rope.

BBC: Aussies clinch tense Twenty20 win

To get the functions right for each cube, he also has to consider how body parts connect, their so-called boundary conditions.

FORBES: Smart Dummies

Although the Boundary Commission, a politically neutral public body in charge of electoral districts, tries to ensure that constituencies are redrawn to reflect demographic changes, in practice, it can't keep up.

ECONOMIST: Bagehot