1. The line that circumscribes the earth and connects all points of highest mean annual temperature for their longitudes. The course of the heat equator varies with the arrangement of continents and ocean currents. It does not even approximately parallel the geographic equator, but ranges from about 20°N in Mexico to about 14°S latitude in Brazil. From West Africa to the East Indies, the heat equator lies north of the geographic equator; from New Guinea to 120°W longitude, it lies south of the geographic equator. 2. The approximate latitude of highest mean annual surface temperature (about 10°N).