Isobars

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. line of constant pressure. Isobars are found ONLY on surface charts. They most commonly connect lines of equal pressure in the units of millibars. High pressure isobars generally occurs with isobars above 1010 mb while low pressure isobars occur with lower than 1010 millibars. Isobars "kink" along fronts and otherwise have a smooth curved trajectory. Isobars represent the pressure at zero geopotential meters. This is done to compensate for elevation changes. Isobars of close proximity represent higher wind speeds than isobars of wide spacing. When isobars are "pack together", this represents an increase in the pressure gradient force and thus stronger winds.
http://www.windfinder.com/grafiken/isobars/isobars_central_europe_1.gif