What is the term for the horizontal measurement of a building layout?

The term for the horizontal measurement of a building layout is accurately described by the term "site plan." A site plan provides a detailed representation of the property's layout, including the position of the building in relation to the boundaries of the property, other structures, pathways, driveways, and landscaping features. It typically depicts the dimensions and scale necessary for understanding how the building will sit on the land, making it crucial for assessing space usage and compliance with zoning regulations.

The other options illustrate different concepts related to construction and design. "Blueprint" refers to detailed architectural and engineering drawings but it doesn't specifically denote horizontal measurements. "Topography" relates to the detailed features of a landscape, including elevation changes, rather than the layout itself. "Elevation" describes the vertical aspects of a building, such as heights and architectural features, instead of its horizontal layout. Thus, a site plan is the most suitable term for what is being described.