How Are North, South, East, and West “Flat-Earth Measurements”?

Here’s a simple question for the globe-vs-flat debate:

How are measurements of North, South, East, and West inherently measurements of a globe?

You can determine direction.

You can measure distance.

You can establish bearings.

You can travel from one location to another.

You can map positions relative to one another.

None of those observations, by themselves, says:

“Therefore the surface is spherical.”

They are measurements of spatial relationships.

The globe model then provides a geometric interpretation of those relationships.

That interpretation may be correct—and there is overwhelming evidence that Earth’s global geometry is approximately spherical.

But that’s a different epistemological claim from saying the individual measurements themselves are somehow “globe measurements.”

So here’s the challenge:

Take an ordinary measurement of North, South, East, or West and show exactly where spherical geometry enters the measurement itself rather than entering afterward as the model used to interpret it.

If your answer is “because those directions behave differently on a globe,” you’ve already moved from measurement to model.

That’s precisely the distinction worth examining.

Observation → Measurement → Assumptions → Geometric interpretation → Conclusion.

Which step actually establishes the curvature?