The Island With No Denominator

The denominator

The occupiers destroyed the records before the surrender, so not even the number of tunnel complexes is known: 19–25 were planned. There is no figure to measure OpenStreetMap against, and inventing one would be the only way to produce a percentage. Every other map of this kind reports what is missing; here the size of the missing part is itself missing.

What is mapped instead

Every fortification you can stand next to is mapped, in German designation order. Almost nothing that runs between them is. One complex — Ho8, the underground hospital — accounts for 36% of it, and Ho8 alone had over 1,000 m excavated. Of 19–25 planned, only Ho5 was ever finished.

The two figures differ because Route du Fort's single ~250 m bore is three OSM ways — a carriageway and a pavement each side. Way length is the reproducible measurement; the second line removes that double-count.

Longest mapped tunnels

Where the underground surfaces

• 397 bunker
• 8 fort
• 7 cave entrance
• 2 battery

Recorded

• 19–25 storage tunnels were planned; the exact number is unknown because primary sources were destroyed before the surrender.
• Only one complex, Ho5, was ever completed.
• Ho8 alone — later the German Underground Hospital — had over 1,000 m excavated, 33.5 m below the surface, for 500 wounded.
• Dug by Organisation Todt, fortress construction battalions and a specialist mining battalion, using forced labourers from North Africa, Russia, Spain and Ukraine.

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