A topographic map displays sea level readings for different locations.
ex. color shows depth
Ocean plate because it is more dense
I guess the "mekong" river.
For continental U.S. the answer is never. Since the earth's rotation axis is tilted 23.5 degrees with respect to its orbital motion around the su, one would have to be less than 23.5 degrees above or below the equator to have the sun pass direclty overhead