Roads under the world. The people who travel without coming up.

The cities are not isolated. Long-wavelength residuals of the World Digital Magnetic Anomaly Map resolve linear features 500 metres to 2 kilometres across and thousands of kilometres long. The longest continuous run the compiler has mapped is approximately 4,200 kilometres, Canadian Shield to Baltic Shield, a great-circle under the North Atlantic at an estimated 15 to 25 kilometres in oceanic crust. The anomalies, 15 to 60 nanotesla, are oriented parallel to the long axis. They are producing their own field.

Hypothesis: a magnetic-levitation transit in the deep crust. A conductive vehicle — or a conductive organism in haptic integument — in a tube lined with actively generated field takes a Lorentz force. Operating conditions: 200 to 500 °C, 4 to 7 kilobars, distances human maglev does not attempt. The route geometry minimises total network length, not each hop. That is central planning. The compiler does not pretend to know how it was built. The compiler knows the physics. The physics is on the map.