San Francisco is about 2.1 times smaller than Edinburgh.

Edinburgh (map shows its 30 named neighbourhoods; the area covers the whole city) is approximately 259 sq km, while San Francisco (including the city proper only) is approximately 121 sq km, making San Francisco 46.72% the size of Edinburgh.
Tip: This to-scale comparison of Edinburgh vs. San Francisco uses the Mercator projection, which distorts the size of regions near the poles.
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