Even those are way too large to represent "city areas" (i.e. metropolitan areas). A more reasonable comparison may be to use their subdivisions, MSA's [0], which can help overcome issues with city boundaries but they too are of course a bit arbitrary and misleading but can also give a better showing of size [1]. I've seen these used in many statistical scenarios concerning population centers.

0 - https://en.wikipedia.org/wiki/Metropolitan_statistical_area 1 - https://en.wikipedia.org/wiki/List_of_Metropolitan_Statistic...