> Eg: consider floors in a building. If you wish to index the horizontal surfaces separating the spaces, it's more natural to start with zero for the "ground le

> Eg: consider floors in a building. If you wish to index the horizontal surfaces separating the spaces, it's more natural to start with zero for the "ground level". It depends. In the USA, 0-indexed floor numbers are the norm. Elsewhere (eg, Australia), 1-indexed floor numbers are the norm.