Abstract: The paper compares the research outcomes of the historical morphological analyses of Detroit, Michigan in the United States of America and Wuhan in the People’s Republic of China, done by the first author and his teams. The two research projects are rooted in thinking about permanence in urban design. The Delft School of historical morphological analysis is applied to the two cases. Central to the method is the production of reduction drawings that simplify the map data so as to express formal structure and identify structural elements on which the cities can base their future development, thus both maintaining permanence, or historical continuity, and local identity. The research is design oriented. As contemporary maps are more precise when compared to historical maps, even when these are recent, the series of maps is constructed working backwards in time. As the urban tissue of Detroit exists almost entirely of extensive grids, that are reductive in themselves, a relatively low level of abstraction from the map data is sufficient to disclose the urban formal structure, and the elements of the urban form that are independent of the grids stand out as the other structural elements, referring to different moments in the urban history. The urban form of Wuhan is much more complicated, and more difficult to understand. Thus its analysis demands higher levels of abstraction, and with that a different set of analytical tools: homogeneous areas and secondary connections. The paper intends to show that when the cities’ physical characters differ, different sets of analytical tools are needed, which results in different research outcomes.