In 1777 de Ferraris issued what was probably the very first topographic map in history of the Austrian Netherlands (currently: part of N. France, Belgium, Luxembourg and the Netherlands).
As a reference point, he used older existing maps of France (made by Cassini de Thury), from where he worked his way up North towards (currently) Belgium and the Netherlands. In order to increase the accuracy of the maps, de Ferraris made corrections, based on a scientifically supported geodesic system (a grid or triangles) which was invented by César-François Cassini de Thury and Giovanni Domenico Maraldi.
Reason for making these maps: mainly military but also political advantage. The order to make the map and funding of it (a huge amount of money) came from the most powerful people of that period (primarily Karel van Lotharingen). The map was later used by milatry leaders, including Napoleon
Of course this does not prove that the Earth is round, but it proves that:
- the accuracy of maps increases when [the] sphericity [of the Earth] is taken into account
- it makes no sense to spread a conspiracy about the spherical shape of the Earth, on the contrary: it would be in the advantage of those who knew that the earth was spherical, if their opponents did not know about the sphericity (or still believed the Earth was flat).
The first point still is valid today.
To some extend, the 2nd point still applies today too, though I'm sure no army exists anymore where the leaders still ignore the sphericity of the Earth.