Some quantity properties "intrinsically" have exact values - like the number of people in a parliament, the number of planets in the solar system, etc. It's confusing to users that Wikibase will guess a margin of uncertainty of +/-1 in such cases.
Considering that this guess would be correct for e.g. the number of square meters in a room, we can't use a general rule for avoiding this problem. We need some kind of hint to the parser what heuristic to apply for guessing the uncertainty. That hint could be
a) A per-property flag (possibly represented by a claim)
b) A separate "amount" or "number" DataType, which would also use QuantityValue, but would have different parsing rules from the "quantity" DataType used for measured values.
Note btw that "population" is a natural number count but should *not* default to exact values, but apply the +/-1 rule.
**Whiteboard**: u=dev c=frontend p=0