These lines will always stay the same distance apart and never meet each other. If they were longer, they'd keep going straight across, or straight up and down. All of the lines that are parallel to the horizon (at right angles to the direction of our gaze) such as the railway sleepers and fence posts-go straight across or straight up and down.
This means that the sides of a road or the sides of a door can both be thought of as pairs of parallel lines. Remember from math class that parallel means running side-by-side, the same distance apart.
The first thing you need to know is that in perspective drawing every set of parallel lines has its own vanishing point. Railway tracks are parallel, but they seem to converge in the distance.
