By David Schepp BBC News Online North America business reporter

As dates go, 11 September is no doubt one that New Yorkers will greet with trepidation and possibly relief as they look back at last year's attacks.

Ground Zero has attracted many tourists

One year after terrorists hijacked two US airliners and crashed them into the twin towers of the World Trade Center, citizens here remain divided over what should become of the 16-acre (6.5 hectare) site where the skyscrapers once stood.

What exactly is to become of the site will be extensively and heatedly debated in the coming months, following the dismissal of six initial design plans.

One concern, that former tenants of the massive office complex would flee Manhattan for good, has not been realised.

Nevertheless, vacancy rates of office buildings in the neighbouring financial district remain high as firms have moved farther uptown, while affordable housing remains as scarce as ever in this notoriously expensive city.

Those concerns along with many others - including a proper memorial to the 2,800 people who died there that day - have put the future of the site in temporary limbo.

Fresh ideas

In planning the future, another date looms - 16 September - the deadline city officials have imposed for submission of design ideas to rebuild the area.

World Trade Center design components

Distinctive skyline Retain twin towers footprints Commercial and retail space Grand promenade on West Street New street grid Central transit centre Residential housing Cultural elements Variously sized open spaces

The request for fresh ideas follows harsh criticism by residents and civic groups over the initial six redevelopment plans.

While each design had redeeming features, all were roundly criticised as unimaginative and too much like the fallen towers.

Advocates for affordable housing complained the original plans did not include provisions for new apartments, a sorely needed commodity in lower Manhattan.

Attracting tenants

In issuing its request for design ideas, the Lower Manhattan Development Corp (LMDC), the entity authorised to oversee the rebuilding of the trade centre, asked entrants to include several design ideas.

Workers clean up for Wednesday's ceremonies

They include re-establishment of the street grid obliterated by the 1960s "big-block" design of the World Trade Center, a much-needed central-transit centre and a grand promenade down West Street.

In its international call for design ideas, the LMDC hopes the final design - due by June - will appeal to as many people as possible.

In doing so, it hopes to gain back former World Trade Center tenants, the majority of which have relocated just a few miles north to midtown.

About 20% of businesses have relocated across the Hudson River to neighbouring Jersey City, Hoboken and other New Jersey communities.

Guiding hands

Rebuilding the World Trade Center involves a bewildering number of agencies, politicians, businessmen, civic organisations and families of victims.

Rescuers have ventured back for the anniversary

The major players include New York Governor George Pataki, who oversees the two state agencies that will guide redevelopment - the LMDC and the Port Authority, which owns the land.

New York City Mayor Michael Bloomberg has much less control over the rebuilding, as he has no official role in the planning process.

In fact the lease-holder of the World Trade Center, Larry Silverstein - who signed a 99-year contract just two months before the attacks - may have more say than any other individual over the rebuilding.

But following harsh criticism of the prototypes for a new centre, Mr Silverstein has fallen largely silent, reneging on his promise to rebuild the towers as they were.

Mr Silverstein remains in a legal battle with his insurers over whether the attacks on the twin towers constitute one occurrence or two - a question that is a matter of billions of dollars.