ELEVATION DATUM ....... Where do I start? Ever wonder how a building gets related to the ground it sits on? Everyone always thinks “siteplan ”. While they are not wrong, they are not complete in thought either. The siteplan sets the house along the “X” and “Y” axis across the ground. How do we establish the height of the building? How does it reference the ground on the “Z” axis (vertically)? W elcome to the Elevation Datum. It’s the reference point that becomes the BASIS for vertical reasoning.