Isobar

http://www.newmediastudio.org/DataDiscovery/Hurr_ED_Center/Hurr_Structure_Energetics/Closed_Isobars/Closed_Isobars.html

Here is an isobar map. The isobars are lines drawn on the map by joining places of equal average atmospheric pressure. In the map above, each line has a pressure difference of (+/-)4 mb.