Where were the first 24 solar terms based?

Twenty-four solar terms are a splendid culture created by the working people in our country, which can reflect the changes of seasons, guide agricultural activities and affect the food, clothing, housing and transportation of thousands of households. Since 2000, the main political activity center in China has been concentrated in the Yellow River Basin, and the 24 solar terms have been established on the basis of the climate and phenology in this area. Due to the vast territory and changeable terrain of China, the 24 solar terms are only a reference for many regions.