Are those boundary lines the actual legal international definition of the borders? Or is it just some convenient representation close enough for ordinary uses?

Are those boundary lines the actual legal international definition of the borders? Or is it just some convenient representation close enough for ordinary uses? You'd think location via GPS or similar framework was easy but it's not nearly as easy as you'd think. Among other things, the land is moving. Both continental plates and then also local features like river beds. See e.g. https://www.youtube.com/watch?v=_TX--Fku9NQ https://www.youtube.com/watch?v=_TX--Fku9NQ