District of Columbia is about 2.9 times smaller than Flathead Lake.

Flathead Lake is approximately 510 km² (197 sq mi), while District of Columbia is approximately 177 sq km, making District of Columbia 34.71% the size of Flathead Lake.
Tip: This to-scale comparison of Flathead Lake vs. District of Columbia uses the Mercator projection, which distorts the size of regions near the poles.
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