3. Paris is positioned at the centre of the Île-de-France
region, which is crossed by the Seine, Oise, and
Marne rivers. The city is ringed with great forests of
beech and oak; they are called the “lungs of Paris,”
for they help to purify the air in the heavily
industrialized region. The city proper is small; no
corner is farther than about 6 miles (10 km) from
the square in front of Notre-Dame Cathedral. It
occupies a depression hollowed out by the
Seine, and the surrounding heights