There should be dictionary entries for "block" that refer to urban street patterns.
A "block" is a not a defined distance in meters, yards, or feet. How far a "block" is depends on how close or far apart the streets have been laid out. In Manhattan, part of New York City, the east-west streets are much closer together than the north-south avenues, so that a "block" or "half a block" is a much shorter distance if you are going north or south on an avenue than if you are going east or west on a street.
So the best we can say about "him" is that he starts work on a house in the middle of a block, halfway between two cross-streets or intersecting streets. When he is done, he goes to a house on a corner. He starts at 1 and then goes to 2.
In the United States, it is very common to have city streets laid out as a rectilinear grid. When streets are laid out this way, as you go along a street you come to intersecting streets that completely cross the street that you are travelling on. In common conversation, the distance along a street between two intersections is a "block". It is not a unit of measurement, and can be of any length.
For example, suppose I were standing at the front door of the Empire State Building. I would be on Fifth Avenue, halfway between 34th and 33rd Streets. It would be half a block north to the corner of 34th Street, and half a block south to 33rd Street. Since the distance between 33rd and 34th Streets is 200 feet, half a block in that instance would be about 100 feet, and walking "one block" along Fifth Avenue would take me 200 feet. Suppose, however, I decided to walk to Macy's department store. I would walk half a block to 34th Street and turn left; Macy's would be one block ahead at the intersection of Sixth Avenue and 34th Street. The distance from Fifth Avenue to Sixth Avenue is 920 feet, so to walk half a block in that direction would be the equivalent in distance to walking more than two blocks if I kept on Fifth Avenue, where the intersections occur more frequently -- but since I had not crossed any intervening street, I would still be on the same "block".
GWB has provided the concrete* data for my more vague "In Manhattan . . . the east-west streets are much closer together than the north-south avenues, so that a 'block' or 'half a block' is a much shorter distance if you are going north or south on an avenue than if you are going east or west on a street."