Pink shading denotes brick structures, yellow for wooden ones.
Above, north of 42nd Street, the Second Avenue frontage is much more developed compared to First Avenue. The blank white quadrant (bottom right corner) was home to Prospect Hill's shantytown of squatters, whose makeshift huts weren't deemed worthy of the map.
Zooming in on the northern side of 43rd Street, site of a varnish factory, a store-house, and the stables of the Second Avenue Railroad Co.
On the south side of 43rd was a depot for the Second Avenue Railroad, a horse-powered railway that naturally enough had its own on-premise blacksmith shop. The railway was replaced by the Second Avenue El in 1880.
Looking south from 42nd Street, there's little development save for a group of rowhouses on either side of 41st Street. They would survive until 1925, when they were purchased and demolished by the French Company. The 3-H's and Essex House now stand in their place.
Zooming in, the only commerce recorded in the area was a slaughterhouse and the mysterious Lamphene along Second Avenue.
See the same area in 1920 here.