In Japan, every han or feudal clan made large maps of their own castle town during the Edo period. These maps have been studied as sources for research regarding the history of urban development. Although most on the research has been focussed on the maps of town plans, it is important to note that they were mainly used to officially distribute house lots to warriors. The purpose of this study is to examine the relationship between the castle town maps and the administration of warriors' residential areas, taking Yonezawa as an example.<br>Maps of Yonezawa during the Edo period changed from large single sheet maps to atlases in the beginning of the 19th century. Large single sheet maps demarcate the boundary of warriors' residential plots and indicate the names of the occupants. The size of the residential plot varies considerably according to the class of warrior.<br>In contrast to large single sheet maps, atlases consist of street maps of small areas. Within them, the names of occupants and their positions in the military organization of Yonezawa-han are written along the street concerned. Accordingly, the difference in actual plot size is not always indicated in these atlases. On some of these names, strips of paper are attached in order to make revisions. Explanatory notes of these maps designate that the names of resident warriors were surveyed every year or two.<br>In addition, these atlases contain two important legends. One of them represents the vacant lots. The other represents the farmlands in warriors' residential areas. Although the warriors were expected to build houses at their own expense on the lots officially provided, some of them were left vacant. Those lands without houses were subject to taxation by the authorities from 1826 and were marked in the atlases. Making use of idle land was one of the policies of fiscal reform initiated from the beginning of the 19th century in Yonezawa-han. These legends are a reflection of this policy.<br>In conclusion, this study aims to show that most of castle town maps were originally practical tools used in the administration of the town itself. They were closely connected with the management of warriors' residential areas, and the appearance of new legends in atlases was due to fiscal reforms and taxation.<br>Similar administrative changes can be found in other castle towns. For example, maps of Kumamoto show that some of the house lots in the warriors' residential areas were marked for taxation as a result of fiscal reform during the latter half of the 18th century. The approach of this study in viewing the changes of castle town maps in relation to administrative reforms should also be valid for the examination of these other castle towns.