The most challenging retail developments are those limited in land area, forced to go vertical. Given factors such as costs much higher than those for a one- or two-level center, convincing tenants to locate several floors away from the street and enticing customers to flow upwards, one might ask: Why would anyone build vertical? The answer is that, when done properly, a vertical retail center is an exciting and dramatic shopping environment.

For a vertical center to be successful, the development team must focus on: location and mix of uses; spatial features; circulation; and tenants.

With the stakes so high in developing vertical retail centers, it is crucial that all four components are fully explored and treated equally. A single weak component undermines the opportunity for success.

Location, location, location: It's central to the success of vertical retail destinations. The few successful vertical retail centers that exist worldwide - Chicago's Water Tower Place, Tokyo's Takashimaya Times Square and Zeilgalerie in Frankfurt - are in intense urban environments with 24-hour activity. CBD locations with high densities of uses, existing vertical commercial and residential development, a substantial residential base and a population that is comfortable moving through dense pockets offer the best chances for success. Historically, U.S. cities have not been 24-hour cities, due to the fact that the work force departs for the suburbs after hours.

Locations that are an integral part of or adjacent to a regional transit hub on the "ant track," as Australians refer to the commuter trail, provide an opportunity to capture additional customers, so long as people are stimulated to move upward through a project. The six-level Myer Centre atop Brisbane, Australia's major bus interchange, benefits from the thousands of commuters that travel through daily.

Superior locations include sites that are near districts that have cultural and civic significance. These districts attract tourists, which also can supply added traffic. However, it is important to note that tourism alone cannot support an urban shopping destination.

Location alone can supply people to the site at street and below-grade retail levels. Additional uses above hotels, housing units and offices create an on-site population that increases shopper traffic at the upper levels. Retail-driven mixed-use developments in urban locations offer opportunity for success, but it is critical that each component have an independent identity and address statement.

Spatial design affects perception The spatial features in a vertical center have a significant effect on the customers' perception of whether they want to be there at all, let alone move upward. The problem with many vertical environments is that everything is uniformly stacked around a single atrium. This allows all levels to be immediately seen, but many customers also find it overwhelming and imposing. At the upper zones, this type of environment can become disorienting.

A vertical center environment should be designed as a sequence of interlocking spaces. Much like a mall has courts, a vertical center should have platforms in the air where activities and gathering for promotional events may occur. These spaces should weave through the center, enticing the customer to intuitively flow up. Creating one- to three-level environments within a five- to six-level center diminishes the perception of verticality and allows the space to be more pedestrian-oriented and intimate. It is critical that the design of these spaces maintains sightlines to tenants and fits within the overall environment.

Circulation - going up It is important to err on the safe side and provide more means of moving upward; this is one area where owners should not scrimp with value engineering. All means of vertical circulation should be easily accessible and visually simple to understand. The success of Water Tower Place is due, in part, to the quantity and placement of escalators and express elevators.

Escalators and elevators must be carefully addressed if they are not to clutter the space and block or hamper critical sightlines to tenants. A strategically placed sequence of escalators that terrace up the retail environment induces upward movement; escalators that dramatically soar through the space turn transportation into an exciting experience. A minimum of three centrally placed elevators should be placed in a center that is over four levels.

The multi-level possibilities A vertical center requires tenants with distinctive storefronts. Multi-level tenants reduce the overall footprint on the more valuable lower level floors and help fill the less sought after mid-levels. Further, they have the ability to create tall, eye-catching shopfronts and add a sense of excitement to the overall retail environment. Examples include the three-level FAO Schwarz at The Forum Shops in Las Vegas and Discovery Channel's multi-level store at the MCI Center in Washington, D.C.

Gourmet markets and cinemas featuring performance houses are powerful anchors. Market environments are a natural to be placed below grade, adjacent to a transit hub, while cinemas should be at upper levels as a vertical draw, with box offices at the mid-levels to help generate traffic.

Today, interest continues to grow in urban revitalization, infill development and serving a population that increasingly desires to live, work and play in the city. While complex, and thus not for the faint of heart, vertical centers are viable and, as proven by successful examples, well worth pursuing.