Zoning was instituted in the early part of this century to restrict nuisance uses of privately owned land. However, long before such restrictions were judicially tested and declared constitutionally legal, it was clear that government intended to regulate land use for other reasons.

More than 100 years prior to passage of Washington's first comprehensive zoning ordinance in 1920, the height of the District's buildings had become a matter of aesthetically motivated public policy. America's founding fathers were much taken by the "look" of Paris, particularly by its low buildings and spacious streets, where sunshine and air were in ample supply.

Keeping the city's profile low was a conscious decision about urban image as well as a matter of safety, access, light and ventilation.

In October 1954, the Supreme Court again confirmed its view that government could control private land use. Congress had empowered the District's Redevelopment Land Agency to condemn property in Southwest occupied by "miserable and disreputable housing." Upholding the right of eminent domain for slum clearance in Berman v. Parker, Justice William Douglas wrote:

"The concept of the public welfare is broad and inclusive . . . the values it represents are spiritual as well as physical, aesthetic as well as monetary. It is within the power of the legislature to determine that the community should be beautiful as well as healthy, spacious as well as clean, well-balanced as well as carefully patrolled . . . if those who govern the District of Columbia decide that the nation's capital should be beautiful as well as sanitary, there is nothing in the Fifth Amendment that stands in the way."

Accompanying this enlarged conception of land regulation has been the advent and growth of highly institutionalized city, county and regional planning efforts. Almost all local jurisdictions in the United States now have planning commissions and agencies staffed by professional planners, as well as zoning commissions and boards appointed by legislative councils.

Planning commissions and planners make "master plans," a phrase conjuring up visions of grandiose utopian designs, authoritative maps of a destiny not to be denied.

Master plans, like zoning maps, are attempts to reconcile the known past with the transient present and uncertain future. Compromised by the urban history that preceded their creation, they try to anticipate land-use needs -- housing, business and commercial, industrial, recreational, educational, institutional, open space and transportation -- and to pin down their future locations, configurations and characteristics.

Land-use plans take on many graphic forms, but the most typical ones are colored mosaics overlaying a base map of the jurisdictional area being planned. Each color represents a different type of land use, and there may be additional symbols for special purposes or sites (such as a transportation center).

Master plans are based on studies of demography and population trends, economic activity, existing and projected infrastructure development (roads and utilities), traffic patterns, and ecological factors (topography, geology, soils, hydrology, climate, vegetation). Planners also consider existing neigborhood patterns and characteristics, taking note of underdeveloped areas or areas perceived to be decaying that may be marked for renewal.

How do master plans relate to zoning, and what is their legal status? In most cities, zoning preceded master planning. Original zoning maps were drawn up to reflect already established patterns of land use and to create additionalreserves of zoned land, usually extensions of existing patterns.

Zoning is law. But a master plan, even though created by an official planning commission and adopted by a legislative council, is a statement of goals and policies about land use, not an ordinance or set of specific, enforceable regulations. Idealized master plans, despite extensive research and analysis, often disregard property ownership patterns. Yet the chain of ownership and platting patterns imposed on urban land is a powerful determinant of the look of cities and neighborhoods.

Land owners and developers often take the initiative and petition for rezoning of property. Justification is usually predicated on at least one of three legal arguments: 1) that the character of the neighborhood has changed substantially; 2) that the original zoning was erroneous or inappropriate; 3) that the proposed new zoning is clearly in the public interest and, most important, in conformance with adopted master plans.

The economic and physical implications of all this can be dramatic. Favorable rezoning can instantaneously increase land value and can change radically the architectural character of development -- building type, size and density.

For example, suppose you owned a piece of property zoned for single-family houses at a density of two dwellings per acre. If lots of this size in this location generally were selling for $10,000, then your land would be worth about $20,000 per acre.

But if it were rezoned for apartments at a density of 40 units per acre, and if the going price for multi-family property was $2,000 per apartment unit, your property would suddenly become marketable for $80,000 per acre -- a 40 percent increase in value.

If you owned 10,000 square feet of downtown property zoned for a maximum height of 65 feet and a floor area ratio (FAR measures the density of the project by comparing building space with land area) of 5.0, you could build a five- or six-story building containing 50,000 square feet. With comparable property selling at $60 per square foot of allowable building area, your lot would be worth $3 million. Rezoning to a height of 110 feet and an FAR of 10 yields a 10-story building of 100,000 square feet and a lot worth $6 million.

Thus, decisions about rezoning are susceptible to pressures unrelated to prevention of nuisances, demonstrable neighborhood changes, aesthetics, or master plan fulfillment. Fortunes can be made overnight on a council's rezoning vote or a commission's affirmative recommendation. Political and economic considerations can influence deliberations, along with the subtle exchanging of gifts or favors.

A sometimes questionable zoning practice, perhaps reinforced by master plans, is premature "spot" zoning. This occurs when a particular property or group of contiguous properties is rezoned to a category of use unrelated to surrounding land uses. Some more intensive and potentially lucrative use seems to have leapfrogged across the landscape onto a "chosen" spot. Setting a new precedent, spot-zoned sites invariably pave the way for subsequent rezoning proposals within the changed neighborhood.

Initially a means for safeguarding property values, zoning statues have become complex, voluminous sets of constraints and opportunities that both entrepreneurs and governments can exploit. Yet even under the best of circumstances, elaborate planning and zoning measures do not guarantee quality architecture or a rich urban environment. By Roger K. Lewis; Roger K. Lewis teaches architecture at the University of Maryland and is a practicing architect.