Do geometric physical boundaries effectively separate groups?

No geometric physical boundaries do not effectively separate groups

Simply put, no.

Geometric political boundaries effectively separate 2 + pieces of

land/territory, but not the people. Take Africa for example. Since

Africa's borders were arbitrarily drawn by the British, they didn't

take the hundreds of tribes in Africa into consideration. Plenty of

Africans were in the same tribe but they were living, and being

separated by, the borders.