The lines connecting points of equal temperature on a weather map are called isotherms. Meteorologists use these lines to provide a wide-range view of temperatures across a region, country or continent. On some weather maps, the area between two adjacent isotherms may be color-coded to represent a particular temperature range.
All of the points that an isotherm passes through represent equal temperatures which were measured at the same time as noted on the weather map. An isotherm that notes a temperature of 32 degrees Fahrenheit is referred to as the freezing level. The usual temperature difference between two adjacent isotherms is 50 degrees Celsius, with the temperatures between those two lines falling into the range between them.
The weather stations supplying the temperature readings for a weather map are rarely located precisely on an isotherm. The temperatures displayed represent a generalization that represents a close approximation based on the exact readings taken at various locations.
Global isotherms run somewhat parallel to latitude lines, particularly during the summer months. Except for the areas near the equatorial line, the increasing absolute plus or minus value of latitude lines results in decreasing isotherm temperature readings. In winter, global isotherms are closer together because of the temperature dropping to a greater degree as the latitude line values increase.