There have been a number of threads on Geodetic Surveyors and how they "prove the earth is a Globe". So many "shot them down" saying that Geodetic Surveyors did not "prove curvature", possibly not, but as I have stated so often Geodetic Surveyors
measured the earth and have done so with increasing accuracy for centuries. The sizes of all countries and the lat/long coordinates of all features have been measured and can readily be ascertained. The most compact source of this information is in maps (some very accurate, others less so) and atlases (often not very accurate, but usually quite close enough).
And it is these measurements that show us the "shape of the earth".
The following assumes that at a given
latitude, a degree of longitude is the same all around the globe. This seems quite consistent with all evidence
[1] and with what is in "the Wiki" on
Finding your Latitude and Longitude.
The following table gives the width of one degree (under the heading "km/deg") at various latitudes in both the northern and southern hemispheres, the circumference of the earth (the distance for 360°) from the map reading at each latitude, the circumference at that latitude based on a spherical earth (yes, I know it's not a perfect sphere!) and the circumference at that latitude based on a Flat Earth Ice Wall Map.
The "Flat Earth Circumference @ Latitude" is based on the 24,900 mile overall diameter of the "known earth" as in
the Wiki, The Ice Wall. The circumferences are then simple "pro-rated" as the meridians on the "FE Ice Wall map" are simply radial lines.
Latitude
| | km/deg @ Lat
| | Map Circum@Lat | | Ideal Globe Circum@lat | | Flat Earth Circum@lat | | Source of "map data" |
51.0° | | 70.3 km/deg | | 25,300 km | | 25,200 km | | 27,400 km | | US 1887 map |
43.0° | | 81.7 km/deg | | 29,400 km | | 29,300 km | | 33,000 km | | US 1887 map |
35.0° | | 91.4 km/deg | | 32,900 km | | 32,800 km | | 38,600 km | | US 1887 map |
0.0° | | 109.7 km/deg | | 39,500 km | | 40,100 km | | 63,200 km
| | Times Atlas map |
-20.0° | | 102.1 km/deg | | 36,700 km | | 37,700 km | | 77,200 km | | Times Atlas map |
-34.0° | | 92.0 km/deg | | 33,200 km | | 33,200 km | | 87,100 km | | 1855 Australian map |
-45.0° | | 79.2 km/deg | | 28,300 km | | 28,300 km | | 94,800 km | | Times Atlas map |
-55.0° | | 65.5 km/deg | | 23,600 km | | 23,000 km | | 101,800 km | | Times Atlas map |
The 1887 US survey map and the 1855 Australian map are very high resolution accurate maps, but the Times Atlas is not such a large scale and not as accurate. Also the figures are scaled (quite accurately) from scanned paper maps, so very high accuracy is not expected. Nevertheless most of the circumferences are within 1% of the expected value for the globe (The "Times Atlas" is a bit out at high southern latitudes - not unexpected for a flat map).
These measurements can be repeated anywhere on earth you like. In many cases, if you have a straight E-W stretch of road you can verify the results yourself. No great accuracy is needed,
as the differences between a globe and the flat earth are massive!But, unless you seriously doubt maps that have been in use for many years, the circumference of the earth gets less as we move North or South from the equator.
To me (as William Carpenter might have said): "this is an incontrovertible proof that the Earth is a globe."
[1] Any navigator would think it ridiculous to suggest otherwise.