Images have a two-point perspective when they have two vanishing points (VPs) present on the horizon line. Seen from the corner, one wall of a barn or a building would recede towards one vanishing point on the left, while the other wall recedes towards the opposite vanishing point on the right, like shown here.
In the picture, two vanishing points are often placed at varied, uneven distances on the horizon line. This explains a different slant of one side of the building in comparison to the other. The closer the VP, the sharper the roof’s and wall’s slant. (In this picture, the right side of the barn has a steeper slant, with converging lines going to a much closer vanishing point in comparison to the left side).
Because of the linear perspective, objects often appear foreshortened, and if you don’t draw them as such, you lose your sense of perspective. Here, horses in the distance become smaller and foreshortened.
http://www.craftsy.com/blog/2015/11/perspective-in-art/
