This study aimed to examine the characteristics and types of reformation of local administrative districts in a metropolitan area, focused on the experiences of Japan, where municipal mergers were carried out extensively over the last ten years. Local administrative districts substantially have spatial characteristics. Therefore, the reformation of local administrative districts should be followed by a detailed analysis of the characteristics of the local area. Unlike other regions, the metropolitan area of Japan shows discriminative characteristics of finance, population and centrality. In addition, there are many types of regional context within a metropolitan area. These could be categorized by finance, population, centrality and basic industry. In conclusion, I revealed that municipal mergers could be categorized by their background and process and many issues were contained in each category. It had a meaning that municipal mergers had characteristics that expanded the regional inequality. Therefore, different approaches considering regional characteristics would be required for a municipal merger to be a useful way for regional development.