Local Governments in Japan make usually use of the groups by similar cities，which based on only Population and the Key Industries，for their financial analysis. But，they have to consider more factors from different standpoints，for example，weather condition，geographical feature，social and economic activities，management of public administrations and financial affairs and etc.，for their big decision making as a merger between several cities. This paper is discussed about what are the structural factors forming groups by similar cities，how much a weight of structural factors changes according to the lapse of time，and how to make a new concept for developing of the groups by similar cities.