San Francisco is about 2.5 times smaller than Durham.

Durham (map shows its 228 named neighbourhoods; the area covers the whole city) is approximately 308 sq km, while San Francisco (including the city proper only) is approximately 121 sq km, making San Francisco 39.31% the size of Durham.
Tip: This to-scale comparison of Durham vs. San Francisco uses the Mercator projection, which distorts the size of regions near the poles.
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