Britische „Minor Possessions in Europe“ (1883)

Heligoland (or Helgoland) is an island right near the coast of Germany. The UK controlled it for most of the 19th century; it was actually traded to Germany a few years after this map was made, in 1890.

https://en.wikipedia.org/wiki/Heligoland%E2%80%93Zanzibar_Treaty

See that neutral ground? We should build an airport!