chart that shows the geographic distribution of the monthly or annual average values of climatic variables—i.e., temperature, precipitation, relative humidity, percentage of possible sunshine, insolation, cloud cover, wind speed and direction, and atmospheric pressure over regions ranging in area from a few tens of square kilometres to global. To minimize biasing the data because of one or two periods with abnormally high or low values, the data are averaged over at least 30 periods, whether they be months or years.