An urban heat island is the name given to describe the characteristic warmth of both the atmosphere and surfaces in cities (urban areas) compared to their (non-urbanized) surroundings. The heat island is an example of unintentional climate modification when urbanization changes the characteristics of the Earth’s surface and atmosphere.
An isohyet or an isohyetal line is a line that joins places of same rainfall on a map within a given time period. A map of isohyets is also known as an isohyetal map.