The ramifications of this statement are as extensive as the statement is brief.  Land is more than a mere physical foundation.  It is vital to man's existence.  It is the source of his food, as well as the foundation for the structures necessary to his social and economic activities.  Because every man uses land, whether he owns it or does not own it, an understanding of real property is based on an understanding of land's utilization by and for man.  The legal theory holds that land includes not only the ground or soil, but everything which is attached to the earth, whether by course of nature, as trees and herbage, or by the hand of man, as houses and other buildings.  It includes not only the surface of the earth, but everything under it and over it.  Thus, in legal theory, a tract of land consists not only of the portion on the surface of the earth, but is an inverted pyramid having its tip or apex at the center of the earth, extending outward through the surface of the earth at the boundary lines of the tract, and continuing on upward to the heavens.  Land provides the foundation for the social and economic activities of people.  It is both a tangible physical commodity and a source of wealth.  Because land is essential to and society, it is important to many disciplines, including law, economics, sociology, and geography.  Each of these disciplines may employ a somewhat different concept of real property.  Within the vast domain of the law, issues such as the ownership and the use of land are considered.  In economics, land is regarded as one of the four agents of production, along with labor, capital and entrepreneurial spirit.  Land provides many of the natural elements that contribute to a nation's wealth.  Sociology focuses on the dual nature of land: as a resource to be shared by all people, and as a commodity that can be owned, traded and used by individuals.  Geography focuses on describing the physical elements of land and the activities of the people who use it.  Lawyers, economists, sociologists and geographers have a common understanding of the attributes of land:  each parcel of land is unique in its location and composition;  land is physically immobile; land is durable; the supply of land is finite; and, land is useful to people.  Real estate appraisers view these attributes as the foundation of real estate's value.  Contrasted with the physical character of land, value is an economic concept.  Appraisers recognize the concepts of land used in other disciplines but are most concerned with how the market measures value.  Markets reflect the attitudes and actions of people in response to social and economic forces.

~ Compiled from excerpts of various editions of "The Appraisal of Real Estate"