ISABNORMAL (or ISANOMALOUS) LINES  , in physical geo- graphy, lines upon a map or chart connecting places having an abnormal temperature . Each place has, theoretically, a proper temperature due to its latitude, and modified by its configuration . Its mean temperature for a particular period is decided by observation and called its normal temperature . Isabnormal lines may be used to denote the variations due to warm winds or currents, great altitudes or depressions, or great land masses as compared with sea . Or they may be used to indicate the abnormal result of weather observations made in an area such as the British Isles for a particular period .