Visionary plans have been created for Washington during the last 50 years -- like the "Wedges and Corridors" and "Year 2000" plans. But none have influenced the capital's actual patterns of growth as much as L'Enfant's original pattern, the McMillan Commission plans at the beginning of the century, and D.C.'s evolving, elastic zoning ordinance.

Like it or not, the zoning regulations, coupled with economic and market circumstances, are by far the most powerful forces shaping the city's nonfederal land use, property values, streetscapes and overall building form.

D.C.'s ordinance, once 20 pages, now contains 300 pages organized into 32 chapters, not including tables of contents and references. And in the spirit of anticipation, 12 of the chapters, having no pages, are reserved for future regulations not yet imagined or drafted.

On the first page of the zoning regulations, their official, adopted title is given:

"REGULATIONS CONTROLLING AND RESTRICTING THE HEIGHT, BULK, NUMBER OF STORIES, AND SIZE OF BUILDINGS AND OTHER STRUCTURES, THE OPEN SPACE AROUND THEM, THE DENSITY OF POPULATION, AND THE USES OF BUILDINGS, STRUCTURES, AND LAND IN THE DISTRICT OF COLUMBIA, AND FOR SAID PURPOSES DIVIDING THE DISTRICT OF COLUMBIA INTO ZONING DISTRICTS."

This mouthful is immediately followed by justification for zoning provisions "held to be the minimum requirements adopted for the promotion of the public health, safety, morals, convenience, order, prosperity, and general welfare . . . "

Their stated purposes are "a) to provide adequate light and air; b) to prevent undue concentration of population and the overcrowding of land; and c) to provide distribution of population, business and industry, and use of land that will tend to create conditions favorable to transportation, protection of property, civic activity, and recreational, educational and cultural opportunities; and that will tend to further economy and efficiency in the supply of public services." Who could disagree?

As of today, there are 30 different zoning districts or classifications (see table). Two of them, the D zone for diplomatic uses (chanceries) and the HR zone for "incentive" hotel and residential uses, are overlay, or floating-zone, classifications. They are applied over and in addition to the zoning map classifications.

There is also a provision for Planned Unit Developments that allow great flexibility in mixing uses, densities, urban design and building types to achieve "sound project planning" and "citywide and neighborhood goals." PUD proposals, applicable to any combination of zoning categories, must be approved by the Zoning Commission after thorough reviews.

Definitions of words and phrases consume 15 pages. Did you know that a "basement" in Washington is the part of a building story below finish grade whose ceiling is more than 4 feet above finish grade, while a "cellar" has a ceiling less than 4 feet above finish grade? Those 48 inches are significant because "gross floor area" of a building, critical to calculating the floor area ratio (FAR), includes "basement" space but excludes "cellar" space.

Do you what an "uptown center" is? It's a "multipurpose major activity center with strong transit orientations and a significant concentration of employment and high-density residential as the principal elements, developed in a manner that serves the surrounding lower density community while protecting it from avoidable intrusions."

You'll have to read the ordinance to learn what is meant by "sexually oriented business establishment" or "specified anatomical areas" (perhaps located near erogenous zones?)

Each chapter defining specific zoning categories begins by spelling out the general intent of the category. For example, the R-2 category "consists of those areas that have been developed with one-family, semidetached dwellings, and is designed to protect them from invasion by denser types of residential development." Invasion?

SP (Special Purpose) districts act as buffers "between adjoining commercial and residential areas . . . to ensure that new development is compatible in use, scale and design with the transitional function of this zone district."

These statements are followed by lists of "matter-of-right" uses, accessory uses, prohibited uses, uses requiring Board of Zoning Adjustment (BZA) approval, and off-street parking and loading requirements. Physical design limitations are stipulated. These include height of buildings, minimum lot dimensions, floor area ratio, percentage of lot occupancy, and widths of rear and side yards and courts.

Building height sounds easy enough to determine, being defined as the "vertical distance measured from the level of the curb opposite the middle of the front of the building to the highest point of the roof or parapet." But what happens when the lot slopes, the street curves, or the building is set back substantially from the lot line? Where's the "middle of the front" with irregularly shaped lots and buildings? The law attempts to answer these questions in a few, well-chosen words.

In commercial and other zones, the ordinance also prescribes procedures for obtaining reviews and approvals by zoning agencies, the Fine Arts Commission and the Planning Office. Special FAR bonus provisions for the Pennsylvania Avenue Development District (for open arcades, enclosed pedestrian spaces, through-square connections, theaters, residential uses and closed courts) are included, along with the criteria to be met by developers seeking density bonuses.

The final chapter, "Administration and Enforcement," charges the mayor with the task of administering and enforcing the zoning law. It cites penalties for violating the law (up to $100 a day for each day of continuing violation), requires proof of zoning compliance prior to issuance of building permits, and requires issuance of a Certificate of Occupancy for any project prior to use, except one-family dwellings.

Like the federal income tax code, D.C.'s zoning code has become lengthy, complicated and highly specialized. Much of it has been written and tailored to implement specific policies -- economic, aesthetic and sometimes sociological -- advocated by the D.C. government and some of its constituents.

Many have welcomed this proliferation of regulations to the extent it has served their interests. Others lament it, either because they find it unwieldy or because they see it as a manifestation of special interests. Could it be otherwise for a city as complex as Washington, D.C.?