NAD83 is one of them. These are all flat coordinate systems. It's taking data from flat systems, because as the "Earth Not Round!" article said, it is these flat systems that are more accurate.

Yes, the article says NAD83 is more accurate than Web Mercator, nothing more:

"Web Mercator's significant weakness is that measurements of distance and area in its native coordinates are completely unusable. Where accurate distance and area calculations are needed, web-mercator GIS data must be temporarily reprojected to a more suitable coordinate system (UTM NAD83)"

So, when you need to calculate distance, reproject from Web Mercator to UTM NAD83 then back to Web Mercator.

According to the article, NAD83 is "...abstracted to a flat, cartesian coordinate system..." from "... the GRS80 ellipsoid and a center-of-the-earth anchor point as its datum..." The source of the datum is not flat.

All this is off topic. ONC charts use neither Web Mercator nor UTM NAD83. They use WGS. They predate WGS84 by decades.

All the links you posted agree, the

**source** of all this data is an oblate spheroid.

That still changes nothing. The specific source of ONC data makes little difference. The charts could have been found petrified in the bottom of a mountain left here by reptilian ancestors. The charts work. They have worked for decades.

The charts closely approximate a sphere. The discrepancies between the conical projection and the spherical source are known and navigators can correct for these when the margin of error must be smaller.

Either the charts are grossly inaccurate or the earth is an oblate spheroid. The videos validates the accuracy of the charts.

The burden of proof has been met again supporting the globe.

Thank you for this forum to share this truth.