The map shows the physical features of ancient Egypt.

A map titled Population Density of Ancient Egypt. A key shows Population Density by color. Green is 200 per kilometers square, orange is 150 per kilometers square, blue is 100 per kilometers square. Green shading begins at the Mediterranean Sea following the Nile River for approximately one-third the length of the river including the cities of Alexandria and Cairo. The next third of the river alternates color: orange, blue, orange, blue, orange, ending at Thebes (Luxor). Green shading begins at Thebes continuing south along the Nile River.

Which physical feature is shaded on the map?

cataract
delta
peninsula
sea