CALL it 29 degrees of separation. That's approximately the angle that the Manhattan street grid is rotated from the north-south axis. And it's the reason that, looking west on the first day of summer, you couldn't see the sun set down the middle of any crosstown street, but you could have on May 28 and can again on July 13.

What inspired the grid itself and provoked New York's angular revolution, whose seeds were planted almost exactly 200 years ago? What biblical injunction or solar cult impelled the city fathers to discard their compasses? Which political, economic and cultural forces unleashed "armies of street openers," as James Reuel Smith, an amateur historian, called them, whose largely uncurbed execution of the grid obliterated much of Manhattan's topography and resulted in the demolition of 40 percent of the buildings north of Houston Street?

It was on July 1, 1806, that the city hired Ferdinand R. Hassler, a Swiss immigrant who would become the first director of the federal Bureau of Standards, to produce a "correct survey and map" of the "island of New York." Just a few weeks later, Hassler pronounced himself indisposed. The Common Council itself, a predecessor of the City Council, was fed up with the obstructions to rational development that were being thrown up by politicians, businessmen and competing property owners — opposition the city fathers described as "obstacles of a serious and perplexing nature."

So city officials did what they often do when they're stymied: they passed the buck to Albany. In 1807, the State Legislature authorized a three-man commission to hire its own surveyor. It is probably apocryphal that the commissioners decided on the rectangular street grid after placing some wire mesh used for screening gravel over a map of Manhattan. But that's pretty much what they suggested four years later when they issued what was known as the Commissioners' Plan of 1811.