Every other door probably leads to a staircase to the second floor. Each ground-floor flat (as they would be called in my home town, San Francisco, since they have private entrances from the street), probably has a front hallway that leads past the cutout for the neighbor's staircase into an apartment that is twice as wide as it seems from the street.

Counting bricks, I estimate a width of 12 feet, 14 tops. One front door per unit. Single-loaded corridor.

Even for railroad apartments, those look narrow--unless there were two stoops per apartment.

Hey! I've been watching for the longest time for some milk on a windowsill. Is that a can of same hanging from above?