World Geodetic System 1984

The World Geodetic System 1984 (WGS84) is an ellipsoid, datum and coordinate system (Archive) which is widely used in cartography, geodesy and navigation fields, including use with Google Maps. WGS84 represents the world with a spherical coordinate system. Such discussions on this topic often revolve around the claim that, since WGS84 provides accurate information and represents the earth as a sphere, it must be evidence that the earth is a sphere.

When assessing these claims it is found that the process is a complex system which pulls information from a large collection of smaller flat maps to provide information to users. The spherical coordinates of the WGS84 are temporarily reprojected onto a map with planar coordinates in order to provide accurate geospatial data.

Geographic Coordinate System
A Geographic Coordinate System is a spherical coordinate system which uses longitude and latitude.

From What are geographic coordinate systems? (Archive) by ArcGIS:

Projected Coordinate System
A Projected Coordinate System is a planar coordinate system.

From What are Projected Coordinate Systems? (Archive) by ArcGIS:

Datums
A Datum is an anchor point which ties two different coordinate systems (geographic and projected) together.

From Datums by ArcGIS (Archive) we read:

State Plane Coordinate Systems and NAD83
State Plane Coordinate Systems are widely used for geographic data, and are based on a flat earth 'plane surveying' methods with simple XY coordinates:

https://en.wikipedia.org/wiki/State_Plane_Coordinate_System (Archive)

Lower down in that article we read that the State Plane Coordinate Systems are associated with the North American Datum of 1983:

The United States Government echoes the same association:

https://catalog.data.gov/dataset/united-states-stateplane-zones-nad83 (Archive)

The Earth is Not Round!
[https://gis.utah.gov/nad83-and-webmercator-projections/ '''The Earth is Not Round! Utah, NAD83 and WebMercator Projections'''] (Archive) By the Utah Automated Geographic Reference Center

Utah's Automated Geographic Reference Center provides an article with a descriptive title of "The Earth is Not Round!" which explains the coordinate systems in use and how the flat earth maps tie into the spherical coordinate systems for data retrieval. NAD83 is the mentioned as the best coordinate system for geospacial data:

NAD83, as we recall above, is based on a planar coordinate system.

On Web Mercator, which is a web-based version WGS84 and is used in services such as Google Maps, the article explains:

We are told that Web Mercator has unusable native coordinates. GIS data is temporarily re-projected onto NAD83 for usable measurement of distances.

If this article were intended to show that the platform is displaying round earth distances and measurements, Utah would surely have titled the article something more along the lines of "The Earth is Round!"

Anchor Point Datum
From the 'The Earth is Not Round!' article it is mentioned "The UTM NAD83 projection uses the GRS80 ellipsoid and a center-of-the-earth anchor point as its datum." It has been asked what the ellipsoid and center-of-earth anchor point that is associated with the NAD83 is referring to. If the NAD83 is composed of state plane maps with a flat XY coordinate system, why is there a reference to involvement of a globe model?

The answer to this is that the ellipsoid and anchor point datum associated with NASD83 is necessary to interconnect with other spherical coordinate systems such as WSG84, in order to connect correctly at the correct location and interchange data.

The article discusses the WGS84 round earth datum:

Note "real world."

The article also discusses the NAD83 flat earth datum:

The passage is speaking of anchor points to connect the two types of systems together.

The accompanying image from the article is the flat map with anchor point:



WGS84 Requires Flat Maps
WGS84 relies on flat projections to give out accurate data.

https://www.gpsworld.com/data-collection-of-wgs-84-information-or-is-it/ (Archive)

As we will recall from the definitions section, a geographic coordinate system is spherical and a projected coordinate system is flat. WGS84 has a spherical coordinate system and NAD83 has a flat coordinate system.

WGS84 itself does not define a projection, and requires a flat coordinate system for operation:

https://www.gpsworld.com/data-collection-of-wgs-84-information-or-is-it/ (Archive)

Next we take a look at the list of projections for the ARCGIS software:

ArcGIS 10.7.0 and ArcGIS Pro 2.3 Geographic and Vertical Transformation Tables (Archive)

This is a long list of the world-wide transformation tables used with ARCGIS, of which NAD83 is listed as one of them. These are all flat coordinate systems and their associated transformations. WGS 84 is taking data from flat systems because, as the "Earth is Not Round!" article describes, these flat systems give out more accurate figures.

Spherical Coordinates Projected To a Plane
We find further references that the process involves projecting a curved surface of geodetic positions onto a plane:

Caltrans Surveys Manual (Archive)

Spherical coordinates are projected to the plane coordinates. Not the other way around. Further, they "must" be projected.

The West Virginia GIS Technical Center (Archive) mentions the same projection of spherical coordinates onto a plane:

We read that the geographic (round earth) coordinates can be projected onto a planar (flat earth) coordinate system to accurately display distances.

The reader should ponder why spherical coordinates are projected onto a plane, and how spherical coordinates projected onto a planar coordinate system could display data and distances accurately if the earth is a globe. If the earth is a globe, the opposite should be true. Projecting spherical coordinates onto a plane should make data and distances more inaccurate, not accurate.

Basic idea behind geographic coordinates
http://www.cadalyst.com/gis/spatial-technologies-mapmaking-and-gis-8853 (Archive)

The article goes on at length to talk about the round WGS84 and the flat NAD83 coordinate systems.

On geographic coordinate systems, the Pacific Northwest National Laboratory says (Archive):

Classified Coordinate Transformations
Of interest, some latitude and longitude coordinate transformations are not publicly known.

http://desktop.arcgis.com/en/arcmap/latest/map/projections/choosing-an-appropriate-transformation.htm (Archive)

Flat Maps as Standard
We find several sources which describe that flat maps and plane surveying are the standard in GIS work.

From https://www.e-education.psu.edu/geog862/book/export/html/1644 (Archive) we read:

A comment by a surveyor named Jerry McGray, RPLS (Archive):