An area of high mountains, as the majority of Viet Nam (especially Northern) separated the Red River Plains and the Southern Plains as the GMS also has a long narrow coastal stretch from North to South.
Areas of Vietnam is mostly high mountains. (Especially the north) between the Red River basin. And southern lowlands of the Mekong River is also a narrow coastal. Long from north to south
The area of Vietnam are mostly high mountains (especially in the North) between the Red River Valley And the southern coastal plains river is also narrow, long from north to south.