Portland is about 7 times smaller than Las Vegas.

Las Vegas (map shows its 26 named neighbourhoods; the area covers the whole city) is approximately 367 sq km, while Portland (map shows its 17 named neighbourhoods; the area covers the whole city) is approximately 56 sq km, making Portland 15.18% the size of Las Vegas.
Tip: This to-scale comparison of Las Vegas vs. Portland uses the Mercator projection, which distorts the size of regions near the poles.
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