Moscow is about 12 times bigger than Boise.

Boise is approximately 221 sq km, while Moscow (map shows its 125 districts within the pre-2012 boundary; the area includes New Moscow) is approximately 2,562 sq km, making Moscow 1,061% larger than Boise.
Tip: This to-scale comparison of Boise vs. Moscow uses the Mercator projection, which distorts the size of regions near the poles.
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