Readily visible on maps and on the ground. Especially common in East Africa. These water boundaries are typically in the center of the body of water, but Malawi and Tanzania have agreed to have the boundary at the north shore of Lake Malawi. This way of looking at the boundaries result from the 19 th century relationship between the British who controlled Malawi and the Germans who controlled Tanzania. Water boundaries offer good protection against attack because generally they are difficult to cross and the person being invaded can see the opposing forces coming and see the gathering of troops.
Water boundaries can be difficult because the courses of rivers can change.
The Rio Grande is a good example. It became the boundary in 1848, but it changed course many times. Ocean boundaries can cause problems because it's been difficult to determine how far into the ocean national influence should exist. This is important because to access to natural resources. The boundaries between some states coincide with differences in ethnicity, especially languages and religions.