The correct answer is isobar.
The isobars refer to the lines of constant pressure. It is a line drawn on a map of a weather linking the points of equivalent pressure. The isobars are produced from mean sea level pressure reports and the values of pressure are illustrated in millibars.
The isobars help in demonstrating that how pressure are changing over space and so assist in illustrating the large-scale weather patterns across a region on the map.
