An isobar is a line drawn through the places with the same atmospheric pressure on a weather map for a specified period of time. The word isobar derives from the Ancient Greek word "baros", meaning "weight". The distribution of isobars is often related to the direction of the wind and can be used by meteorologists to predict future weather patterns. Isobars are commonly seen during weather reporting on television.

Meteorological contour lines such as isobars are based on data received from weather stations or weather satellites at various points across the Earth. The lines are drawn approximately based on the information available.

As well as atmospheric pressure, contour lines can represent the places on Earth with the same temperature (isotherm), equal rainfall (isohyet), or wind speed (isotach).

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