To grasp the characteristic of distribution of meteorological condition for the design of air conditioning systems within a certain district, a series of analyses about temperature data measured by local government and AMeDAS data, were performed. By statistical analysis, six kinds of isothermal graphs covering 100 km Tokyo district, were obtained. A method estimating daily variation of air temperature inside the area of isothermal graph, was proposed. Accuracy of the proposed method using six isothermal graphs was confirmed, comparing with AMeDAS data. A series of field measurement data using trains of JR line within the Tokyo district were shown. A method for transfering from field measurement data to design temperature data was proposed, and validity of the method was confirmed.