This is an amazingly creative use of all the iPhone technologies, and New York is one of the densest places in the world so this would definitely be very helpful. It's not helpful for locals (who have the lines memorized), but for travelers who get confused and turned around in the maze of skyscrapers... this will be a great help.
I wonder if the technology is easily extensible to take new maps and locations. Post that openly and watch the world start creating further content... not just more subway maps, but more geographical locations (restaurants, hotels etc).
When I lived in New York I looked into mass producing a compass that was marked "Uptown/Downtown" (in place of North/South) and "Eastside/Westside" (in place of East/West) with the North/South line correctly aligned at 29.8 degrees from the actual.
You can hand these to visitors and they'd instantly be able to tell which direction to walk when stepping out of the subway.
I smell an iPhone app. Uses GPS to determine what city you are in and then displays direction in local terms. I want one. This could even work in Boston where the North End is mostly east of City Hall and the South End is a couple of miles west of South Boston
I wonder if the technology is easily extensible to take new maps and locations. Post that openly and watch the world start creating further content... not just more subway maps, but more geographical locations (restaurants, hotels etc).
Exciting!