"It is like the billboarding of the novel," said Letty Cottin Pogrebin, president of the Authors Guild.

With buses and subways plastered with advertising, the planned billboarding of the Port Authority Bus Terminal, and the invasion of schools with commercial messages, the question is, What is next?

In three-dimensional scenes, the term billboarding is applied to a technique in which objects are sometimes represented by two-dimensional images applied to a single polygon which is typically kept perpendicular to the line of sight.

"Most of the stores on Madison are a form of retail billboarding, similar to the Warner Brothers or Disney store or Niketown," says Paco Underhill, managing director of Envirosell, a behavioral research and consulting firm that specializes in retail shopping patterns.