Which of the following features affects inter-visibility between two settlements?

The feature that affects inter-visibility between two settlements is a high hill. When settlements are located on opposite sides of a high hill, they are not able to see each other due to the obstruction of the hill. This lack of visibility can have both positive and negative implications. For instance, it can hinder communication and trade between the two settlements, but it can also provide protection and privacy. In contrast, a deep trench, broad valley, or wide river may not necessarily affect inter-visibility between two settlements, as they can be bridged or crossed, or there may be clear lines of sight between them.