Köppen began a systematic study of the climate and also experimented with balloons to obtain data from upper layers of the atmosphere. In 1884, he published the first version of his map of climatic zones in which the seasonal temperature ranges were plotted. It led to the development of the Köppen climate classification system around 1900, which he kept improving for the rest of his life. The full version of his system appeared first in 1918; after several modifications, the final version was published in 1936.