How to Create Isobar Maps
- 1). Find the lowest pressure marking on the map. If there are multiple low pressure points separated by higher pressure areas, they represent different pressure areas and should be treated separately.
- 2). Draw a continuous line through all the adjacent points of equal pressure. Depending on how the map is marked, you may have to estimate where the point is. For example, if you are drawing an isobar connecting points at 1,000 millibars of pressure, it would go about halfway between two points that are marked 997 and 1003.
- 3). Continue drawing lines at 4 millibar increments, or the increment of your choice. Each line should either form a closed loop or end at the edges of the map. No lines should cross each other, but in situations where they would, create two separate isobars. Mark each isobar with the pressure level it represents.
- 4). Mark the center of every low pressure area with an L and every high pressure area with a an H.
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