An apartment, according to the dictionary, is a "suite of rooms" in an apartment building. But not all apartment units seem like "suites."

Apartments, whether inhabited by the rich or the poor, come in endless varieties, ranging in size from tiny, one-room efficiencies to villalike, multilevel penthouses. Most common are one-, two-, and three-bedroom "flats" that are easily stacked and packed in apartment buildings.

A certain spatial sameness pervades many types of apartment units, whether in suburban garden-apartment complexes or downtown high-rises.

Most units contain a kitchenette or kitchen, plus one or two bathrooms and, with few exceptions, an insufficiency of closets and storage. Living and dining areas often are combined into one space, frequently with only the living area adjacent to windows. The dining area may be little more than an interior alcove, dog-legged off the living room and adjacent to the kitchen. Except for the living room and bedrooms, everything else -- kitchen, baths, closets -- abuts the interior, windowless wall separating the unit from the public corridor.

In units with two or more bedrooms, there is almost always a "master" bedroom, so-called because it has more area, more closet space, perhaps a dressing area, and maybe its own "master bath."

Efficiency apartments, containing from 250 to 400 square feet, can be the most economical inefficient unit type. This occurs because the costliest components of any apartment are its kitchen, bathrooms, plumbing and heating and air-conditioning equipment. Just building bedroom square footage is relatively inexpensive, adding suprisingly little to the total unit cost beyond the basic core components and systems costs.

Yet rental rates tend to escalate dramatically with each additional bedroom, much faster than cost increases arising from bedroom construction. For example, building a 400-square-foot efficiency apartment, with kitchen and bathroom equipment comparable to larger units, can cost nearly as much as building an 800-square-foot two-bedroom apartment. But the latter may rent or sell for more than twice the former, making it the more profitable unit for the landlord or developer.

Graciousness in an apartment depends more on the size, dimension and proportion of rooms than on room count. Who hasn't been in an apartment where spaces felt excruciatingly tight, narrow or claustrophobic?

The entry vestibule, if there is one, may have a coat closet just big enough for one coat. If two or more people arrive or depart simultaneously, such vestibules can become gridlocked.

Many apartment kitchens seem designed to accommodate one very thin person. Opening the door of any of several appliances -- dishwasher, refrigerator or oven -- or pulling out a drawer may render the entire kitchen momentarily unusable. Often the apartment building's mechanical ventilation system, which supposedly exhausts air from kitchens, seems to work in reverse, drawing in alien odors produced elsewhere.

Interior corridors, normally about three feet wide, lead to bedrooms and may function well if perfectly straight and dimensioned properly by the contractor. But let there be a bend or two in the corridor, or shrink its width a couple of inches, and your shoulders will rub constantly against its walls, knocking pictures out of alignment, while your shoes scuff the baseboard paint. Of course, the biggest thrill with such passageways comes when moving furniture.

And how many unfurnishable rooms have you been in? How often have you seen a living room in which traffic patterns, doorways, windows and perhaps a fireplace left you nowhere to arrange furniture sociably or hang art work? Countless are apartment bedrooms, where closet, door and window locations prevent reasonable placement of anything but a narrow bed or where the only place for a large bed is against a window.

Apartment units don't have to be like submarines. Architects and developers can create delightful interior spaces that are shapely, comfortable and commodious simply by making the available space pay higher dividends. Combining or overlapping spaces -- living, dining and kitchen areas -- is probably the tactic most frequently used to make small rooms look and feel bigger. But careful planning and dimensioning, especially in entries, halls and kitchens where inches are critical, can make a big difference.

Because space in most apartments is at a premium, placing doorways, closets and windows is crucial. Their placement affects not only practicality, but also spatial perception. Windows, by their size and position, can make rooms seem smaller or larger, or they can reinforce a room's geometry. Generous views and access to the outside, via a balcony or terrace, can extend interior space into the landscape, perhaps making modest rooms grander.

With larger windows, natural light will penetrate farther into an apartment's depth. In fact, the relationship of rooms to windows and room proportioning are what limit the overall depth (the distance from window wall to public corridor wall) of most apartments. This depth varies from 25 to 35 feet, typically the sum of the dimensions of one room, the unit's private hallway and one bathroom.

Many apartments have balconies. Some are like small outdoor rooms, airy open places to sit, socialize, barbecue or grow plants. But with low ceiling heights, opaque railings and solid walls flanking either side, balcony spaces, though private, can be compressive, dank and somber, ideal for growing mushrooms. The light quality within living spaces behind such balconies likewise can be gloomy.

A lot of balconies are too vestigial, so small as to be virtually useless. And often balcony railings seem shaky, conveying the impression that, should you be foolish enough to lean against them, both you and the railing will disappear. Like any space, a balcony's design qualities -- size, proportion, accessibility, openness and detail -- will determine whether people or snow tires sit on it.

Apartments are typically sandwiched between floors that limit ceiling heights to eight feet, among the more constraining architectural factors. This greatly restricts the potential for volumetrically shaping spaces in three dimensions. Thus, most apartment designers do little more than arrange partitions to create reasonable room layouts and efficient circulation.

However, with slight increases in the floor-to-ceiling dimension, design possibilities increase dramatically. Architects can play with contrasting ceiling heights -- coffers, domes or vaults can be introduced over special places and spaces. Decorative elements on walls, coves, bases and cornices can be more sculptural. Even floor levels can vary.

Sometimes architects design duplex apartments, occupying two floor levels interconnected by a private, interior stair. Like a town house, one level can contain bedrooms while the other contains living, dining and kitchen areas. Most important, two-story spaces can be developed. Buildings with duplex apartments may have alternating floors without any public corridors or elevator stops (called "skip-stop" buildings).

Doing more than the conventional, going beyond the minimal, is likely to cost more and therefore lead to higher rents or selling prices. Nevertheless, much apartment construction is done routinely with little effort given to making the best possible living units using available resources. Even small, simple gestures, measurable only in inches or perceivable only as detail, can go a long way toward transforming an apartment "unit" into an apartment "home."

NEXT: Atypical housing types Roger K. Lewis is a practicing architect and a professor of architecture at the University of Maryland.