The line of sight analysis uses a polyline as input. From an observer’s point of view, it determines where they have a clear view. The tool cuts the line up into obstructed and non-obstructed sections.
Because line of sight determines what is visible and hidden along a line, the input is a polyline. Also, it’s important how you draw the line. For example, the order you draw vertices determines the start and end point of the visibility analysis.