This information is then used to draw an isobar chart. An isobar chart like the one shown above shows lines of equal pressure and also indicates where the pressure is low and high. Study the map carefully and decide what the pressure will be at X . Different lattitudes of the Earth are heated at different rates creating areas that are warmer or cooler than others. In warm areas the air is heated and rises causing a drop in pressure.
Air is sucked in like a vacuum cleaner from surrounding areas where the pressure is higher.
This movement of air from one place to another is called wind. The areas where pressure is higher are usually cooler areas. When air is heated it rises to form clouds and rainfall. Pressure drops and an area of low pressure forms. When the air rises, air from surrounding areas rushes in to replace the rising air.