Thunder Bay is composed of Port Arthur and Fort William, both settled in the 1880s.
Port Arthur, 1891
Fort William, 1913
Like many land survey maps of this type, many of those streets never got developed. The left half of the Port Arthur map was only about a third developed (and a new street runs through it on a funny angle), and in the Fort William map, much of what is shown on the left half wasn't built until the 1950s.