Flat(ter) here referring to the Earth as an ellipsoid, not an actual flat thing, in case people were wondering. Really enjoyed reading this, hadn't even realised how complex the political and technical practicalities of measuring the Earth were in the early 19thC.

Also, a much easier read than Pynchon's Mason and Dixon [0]

[0] https://en.wikipedia.org/wiki/Mason_%26_Dixon

> In its own day, the Arc crossed only one international border, between Sweden-Norway and the Russian Empire.

Looking at the map, it's not really clear why they decided to veer west to Swedish(-Norwegian) side of border instead of sticking closer to the Tartu meridian and staying within Russian(-Finnish) borders, terminating somewhere near current-day Utsjoki. Does anyone know the rationale for the route?