Buenos Aires is around the same size as Des Moines.

Des Moines (map shows its 58 named neighbourhoods; the area covers the whole city) is approximately 228 sq km, while Buenos Aires is approximately 203 sq km, making Buenos Aires 89.04% the size of Des Moines.
Tip: This to-scale comparison of Des Moines vs. Buenos Aires uses the Mercator projection, which distorts the size of regions near the poles.
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