We live in an extremely thin spherical shell, not in a sphere

The highest city is 5,100m altitude; a 1hour walk were it straight up

In 1998, 1.9 billion or 34% of humans lived within 100m altitude of sea level

The ocean averages 4 km deep

10% of Earth is continental shelf, only 100-200m deep

Again, we are confined to the bottom 2 meters of the ground

Deepest SCUBA dive is 332 m, Burj Khalifa is 2700 m

So to be generous we can span 3km from the surface, a 36 min walk