Isobars

Isobars measure lines of equal barometric pressure on a map. Barometric pressure is a measure of air density against a surface on Earth. This is important in fields such as meteorology as this effects air temperature and is important in understanding climate. The isobar map below shows the barometric pressure in the Great Lakes area of the United States.





http://ww2010.atmos.uiuc.edu/guides/maps/sfcobs/cntr/gifs/bars1.gif