21.) Isobars

Isobars:

http://z.about.com/d/german/1/0/1/J/aWetteurfronts.jpg

An isobar is a line of equal or constant barometric pressure on a graph, plot, or map. In meteorology, the barometric pressures shown are reduced to sea level, not the surface pressures at the map locations. The distribution of isobars is closely related to the magnitude and direction of the wind field, and can be used to predict future weather patterns.