In the field of meteorology, it is very important to know the behavior of atmospheric pressure, the strength of the wind and the direction it takes in a certain geographical area. In this sense, there are maps that show these elements of the climate through graphic representations called isobars , which are drawn as lines that indicate the pressure in a given space . These lines allow the identification of anticyclonic or depression zones. Likewise, it should be noted that these lines are drawn from the data generated by the meteorological analyzes carried out at the measurement stations.


What are isobars?

In general, the term isobar is used as a noun that designates a curve that represents pressure points on a map , graph or plot for the purpose of precise identification. Likewise, it is important to note that the word isobars can also refer to a surface on which the pressure maintains the same value at any point. In this sense, it is important to distinguish an isobar line that can be drawn on any non-isobar surface, from an isobar surface, on which isobar lines may not appear, since the pressure is constant at any point.


The term isobar is a compound word that comes from the Greek and means “Iso” equal and “bara” weight. In this sense, the isobar is defined as a line that encompasses the areas where the atmospheric pressure is equal.

  • History of isobars
  • What are isobars for?
  • Isobar map
  • Interpretation

History of isobars

In the history of cartography, isobars are a type of isolines , that is, curved or straight lines that connect the geographical points where the function has the same constant value. In the case of isobars, the function is atmospheric pressure.

Weather maps have their origin in the mid-nineteenth century in the United States . American physicist Joseph Henry was the first to expose a weather forecast map of the lower Ohio River from the Atlantic coast.

At present, meteorological maps with their isobar records are of great help in the marine and air transport industry since this type of cartography allows us to know if there are adequate conditions to make trips by sea or by air without the life of crew members are at risk.

What are isobars for?

Isobars give information about the direction and strength of air masses in a given area .

In meteorological maps they are represented as lines that join all the points where the atmospheric pressure is equal. Atmospheric pressure has millibars as units of meteorological measurement. Isobars measure in 4 millibars intervals. A normal pressure is in the range of 1013 millibars, while high or low pressures are in ranges greater or less than 1013 millibars.

Isobar map

Isobar maps draw geographic spaces where the behavior of atmospheric pressure, the force of the wind and the direction it takes in the spaces described by the map are represented.

On the geographical area of ​​the map, the isobar lines or pressure isograms are placed, which are curves that group the points that have an equal or constant atmospheric pressure.

In meteorological maps, different types of curved lines can be identified, isobars, alobars that can delimit the change in atmospheric pressure in a given area. If the pressure change is positive, the curved lines will be called an analobar, but if this change is negative it will be called a catalobar.

The value of isobars is expressed in millibars or hectopascals (hPa) (1 hectopascal = 1 millibar).


To interpret isobar maps, it is important to identify the behavior of the wind and atmospheric pressure through the proximity or distance of the pressure lines in specific areas of the represented cartography.

If the lines are close together, it means that the wind will blow hard , that pressure changes occur quickly, and that there is a large difference in atmospheric pressure over a small space. If, on the other hand, the curved lines are far apart, the wind force will be reduced , the pressure changes will occur slowly and there will be a balanced pressure in a larger space.

In an isobar map (pressure map), the low pressure center is identified by the letter B while the high pressure center is identified by the letter H.

To read an isobar map it is important to:

  • Learn the basics of rainfall
  • Know how to interpret the actions that occur as a result of changes in atmospheric pressure.
  • Know the symbols of atmospheric pressure.
  • Interpret the behavior of high pressure systems.
  • Interpret the behavior of low pressure systems.
  • Recognize the movements and types of fronts (cold, hot and occluded).
  • Analyze the behavior of hot fronts.
  • Analyze the behavior of cold fronts.
  • Analyze the behavior of the occluded fronts.

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