How does Ron Chernow use imagery in Titan: The Life of John D. Rockefeller, Sr?

Imagery:

Each morning, he left his boardinghouse at eight o'clock, clothed in a dark suit with a high collar and black tie, to make his rounds of appointed firms. This grimly determined trek went on each day—six days a week for six consecutive weeks—until late in the afternoon. The streets were so hot and hard that he grew footsore from pacing them.