Isobars are lines that connect points of equal pressure on weather maps. The word originates from Greek, where isos means equal and baros means weight. Isobars are designed to describe the horizontal pressure distribution of an area, and are created from mean sea-level pressure reports. Because most of the weather stations are not located at sea level, but at a certain elevation, the pressure measured at every location has to be converted into sea level pressure before the isobars are drawn. This normalization is necessary because atmospheric pressure decreases with increasing altitude, and the pressure difference on the maps has to be due to the weather conditions, not due to the elevation differences of the locations.

Isobars are similar to height lines on a topographic map, and they are defined such that they can never cross each other. An important consequence of air pressure differences is wind, because...