John will spend the night at his aunt’s place. She has just moved to the city, but she forgot to tell John the house number. All he’s got is a map with the building’s outline. Which house does it match?
Cartography is complicated and expensive work – it’s not surprising that map publishers keep a watchful eye on their copyright. To that effect, maps sometimes include “trap streets” – streets that don’t exist in reality but are a dead giveaway if some rival publisher simply copies a map.