In the simplest form of perspective, all lines running perpendicular to the horizon culminate in a single vanishing point. This one-point perspective is how a viewer perceives an object that is directly facing them, without angle. To create a one-point perspective, first draw a horizontal line to indicate the horizon and place a single dot at some point on it. All lines receding from the viewer will angle towards this vanishing point. Imagine standing in an alley, and its sides receding towards a single point directly ahead.
A two-point perspective allows an additional set of parallel lines to culminate in a second vanishing point. It's also known as an "angular perspective," because it shows objects placed at an angle to the viewer. Visualize facing the corner of a building. The corner's edge runs vertical, while one wall recedes towards a single vanishing point on the right and another wall recedes to the left. Like a one-point perspective, both vanishing points must reside on the horizon line.
When viewing an object, a keen observer will notice that vertical lines angle towards a single point. This vanishing point floats in space above or below the horizon line, yet never outside the other two vanishing points. If the vanishing point is below the horizon, the "bird's eye" perspective suggests the viewer is looking down upon an object. A "worm's eye" perspective places the viewer below an object with a vanishing point above the horizon.
In everyday life, and most artistic depictions, the one-, two- and three-point perspectives are most widely seen. However, it's possible to perceive objects with up to six vanishing points. The four-point perspective utilizes two vertical vanishing points, with one below and one above the horizon line. The result is a curving, oblong-esque object. A five-point perspective creates a circle to depict all objects in 180 degrees of space. This resembles the image seen on a mirrored hemisphere. However, a six-point perspective uses two circles, to depict the full 360 degrees of space surrounding a viewer.