Isobars

http://ww2010.atmos.uiuc.edu/(Gl)/guides/maps/sfcobs/cntr/wind.rxml

Isobars are lines that connect points of equal atmospheric pressure. The lines never cross or touch on a map. They are useful in tracking low and high pressure systems. In the map above of the East Coast of the United States, shows a large low pressure system traveling in the northeast direction.