ISOBAR, a line upon a map or pressure chart connecting places having the same atmospheric pressure. The pressures can either be "reduced to sea-level" by means of a calculated factor, or can be in the form of unaltered barometer (q.v.) readings. A general pressure map is intended to indicate by isobars the "reduced" average pressure, for any selected period over large areas, while the daily weather charts for smaller regions show the presence of cyclonic, anti-cyclonic, or other such temporary sys tems. Isobars should be interpreted as the intersections of in
clined isobaric surfaces with the surface of the earth.