My home town of Chichester is officially twinned with Chartres in France. In my youth there were school exchanges, mayors gave speeches at each others' festivals and stuff. Nothing elaborate, but the link seemed to make some sense. Both cities have Roman history, famous cathedrals, are not too far apart and are roughly the same size.
But the bigger the city the less sense it makes. Mexico City is twinned with the usual plethora of capitals around the world: Beijing, Berlin, Brussels, Bogota, Buenos Aires and some 50 others. But what do they actually do together? Particularly puzzling is its twinning with Andorra la Vella… The world's most and least populous capitals?