Former president Grover Cleverland, once cynically said, "What shall be done with our ex-presidents? It has been suggested that they be taken out in a five-acre lot and shot."
Here, why "five-acre"? Is there any cultural implication? Or does it mean just a small area?
I'm not aware of any special cultural or historical meaning to "five-acre lot." 5 acres is about 2 hectares. It would be rather large for a residential building lot, so it implies a small agricultural field, perhaps a handy one near the barn. I suppose it is what would be done with a useless, broken-down old horse in the 19th century—take it out of the barn into the adjacent field and shoot it.
If it had any special meaning when Cleveland said it (presumably, some time between the end of his second term on March 4, 1897 and his death on June 24, 1908), that meaning has not survived.