San Francisco is about 3.4 times bigger than Rockville.

Rockville (map shows its 87 named neighbourhoods; the area covers the whole city) is approximately 35 sq km, while San Francisco (including the city proper only) is approximately 121 sq km, making San Francisco 244% larger than Rockville.
Tip: This to-scale comparison of Rockville vs. San Francisco uses the Mercator projection, which distorts the size of regions near the poles.
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