Isobars are lines that connect places at the same pressure.
You will also be introduced to what is called the simple surface-station model. To determine the actual pressure in millibars, this number must first be decoded. If the number is between 56.0 and 99.9, add a leading 9 . We'll discuss some of the other numbers and symbols at a later time. It is unlikely that many stations will report exactly 1004, so you will need to do some estimating.