San Francisco is about 2.9 times smaller than Atlanta.

Atlanta (map shows its 114 named neighbourhoods; the area covers the whole city) is approximately 350 sq km, while San Francisco (including the city proper only) is approximately 121 sq km, making San Francisco 34.52% the size of Atlanta.
Tip: This to-scale comparison of Atlanta vs. San Francisco uses the Mercator projection, which distorts the size of regions near the poles.
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