Poking around in Google Maps, I noticed that Serris, the town in which Disneyland Paris is located, has a circular ring road. And I mean nearly perfectly circular. Looking at it through Street View, it becomes apparent that even there, the curve (well, the bend) is very hard to see. In town, where the field of view is more restricted, it isn't even noticeable. https://firstname.lastname@example.org,2.7868241,5619m/data=!3m1!1e3 Now, in the more open areas, you do see a slight bend. But the perpendicular curvature, as in looking out instead of along the curve, is basically undetectable. This looks by all means as the edge of a straight road, even though it's very slightly curved. Now, this is for a 2D section of a sphere with a radius of slightly more than 1,5 km. Earth's radius is more than 6000 km, and the FEs don't get why they don't see any curvature. The equivalent would be that of an ant on the edge of that road trying to realize that it's curved, or perhaps even worse in terms of scale.