The Mannahatta project is basically an extremely detailed computer simulation of what Manhattan might have looked at on the eve of European discovery. The graphics are particularly cool.
That said, I think the project is a lot more interesting than the book. The book is okay, just rather plodding. It seemed like the author really didn't have that much to say and padded the book out with some very generic, rather flowery prose. Here's an example:
"Yet it is exactly these processes of destruction that keep nature refreshed and alive. Take the death of one of those huge old-growth American chestnuts on Mannahatta, perhaps already 350 years old that night that a big wind knocks it down. The next morning, the gap in the forest canopy floods the ground with sunlight, and all those younger trees that have struggled in the shade through the decades are let loose to grow as fast as they can toward the light. In the course of the twenty years it will take the trees to fill the place of that mighty chestnut, the sun-drenched meadow will accommodate ephemeral flowers and insects that wait for just this chance to reproduce. The meadow is drenched with birdsong from nests that dot its fringes; white-tailed deer graze the lush secondary growth, where wolves come to hunt. Even the dead body of the chestnut, laid to rest in the undergrowth, becomes a habitat for mushrooms and insects, the perfect burrowing place for chipmunks and ground squirrels - until a weasel comes to ferret them out. At night a great horned owl silently falls on the timid deer mouse, and the frost descends beneath the starry sky to eclipse delicate flower buds where once the mighty chestnut grew."
How much better it would have been if he had talked a little bit more about the project or about Manhattan. Just as an example, there is an excellent map of the streams that existed in 1609, but only about a page of specifics on them. Instead, we get this:
"Streams are the conduits for water flowing aboveground; springs form where the underground water flow breaks the surface. Both are fed by rainwater and snowmelt. The rain falls, running down the leaves, stems, and trunks of trees (known respectively as leaf flow, stem flow, and trunk flow; trees can hold up to nearly a quarter inch of rainfall, which is why they are a convenient place to hide when it begins to rain, but not later)..."
Ironically, there is a whole appendix devoted to moer specific info. Why wasn't that tied in to the main body of the text?
One final gripe ... In general, the illustrations are knock-outs. Some of the maps, though, are uninterpretable. Take, for example, the one on ecological communities, on p. 139. It shows 44 different communities, in 44 different shades of brown, green, and blue. How we're supposed to distinguish one from the other on the map is beyond me.
Overall, I think this could have been a great coffee-table book or a real read, but ended up trying to be both, and never really succeeded at being either.