There are those, like Ward Churchill or some people on the paleo-con right, who feel New York had it coming on September 11, 2001.The city is the heartless center of a ruthless globalism that seeks to extirpate the small, the local, and the authentic, wherever they may be rooted out. New York is this, New York is that — in online forums, in magazines, people speak of the city as though it were some monolithic Moloch marked by the anomie and rootlessness of its population, each member of which is a cog in the wheel of the Empire.

Kevin Walsh started his Web site, “Forgotten New York,” in March 1999. It rapidly became one of the most popular New York City-related Web sites, with a core viewership of fanatical devotees who, like Mr. Walsh himself, see and live in another New York, a city with a past, and a city of parts, where the small, the local, and the authentic exist in as great abundance as you please.

It was only a matter of time before a publisher got wise to the Kevin Walsh phenomenon and asked him to cast “Forgotten New York” in book form. Subtitled “The Ultimate Urban Explorer’s Guide to All Five Boroughs,” Mr. Walsh’s new book is organized by borough, with 50 pages on the Bronx,84 pages on Brooklyn, 78 pages on Manhattan, 78 pages on Queens, and 70 pages on Staten Island. Such a breakdown has got to be a first for a book on New York. (It makes you wonder what Mr. Walsh has got against the Bronx.) By contrast, the “AIA Guide to New York City,” long venerated for its close attention to the non-Manhattan boroughs, has, in its most recent (2000) edition, 540 pages on Manhattan, 91 pages on the Bronx, 162 pages on Brooklyn, 82 pages on Queens, and a whopping 48 pages on Staten Island.

Granted, the two books are dissimilar in intention. The “AIA Guide” focuses on architecture, of course, while “Forgotten New York” focuses on . . . well, anything and everything that has ever caught Kevin Walsh’s eye. Sometimes it’s architecture; more often, it is some architectonic or semiotic remnant that serves as a de facto memorial of the city’s past. Another difference is that the “AIA Guide” is written from the point of view of two professional architects, Elliot Willensky and Norval White. “Forgotten New York” is the undertaking of an amateur of the urban scene. And by “amateur” I mean a “lover.”

Both books exemplify what I call “urban epistemology,” or the various ways of knowing the city. In 1961 (the same year as Jane Jacobs’s “The Death and Life of Great American Cities”), the urban planner Kevin Lynch wrote an influential book,”The Image of the City,” in which he polled people in several cities on how accurate their mental maps of their own cities were. His presumption (a correct one, in my view) was that the less accurate the map, the likelier the city was to be a dispirited, undynamic place. The people of Jersey City, as I recall, scored very low. The people of Boston scored very high. (NewYork was not included.) Boston (and this was well before its much publicized “renewal”) had a strong image, with a lot of specificity to it. A city presents itself to its people (and to outsiders) as being worth knowing, or not.

The boom, since the 1970s, in urban guidebook-making (as well as in related phenomena like walking tours, which Kevin Walsh occasionally leads), has made one thing manifestly clear: New York strikes very many people as worth getting to know. The “AIA Guide”led the way (its startling first edition appeared in 1968) in providing a very close-grained appreciation and mapping of the city, the book’s sheer bulk and number of entries giving off a whiff of comprehensiveness. But for all its content, it couldn’t possibly be comprehensive. Mr. Walsh aims at nothing of the sort. His book is, as Gay Talese subtitled his own book on New York, “a serendipiter’s journey.”

And what a journey. The book can be faulted on some grounds. Some fans of the Web site might miss its joyous anarchy, which is absent in the book, where the entries are clearly laid out and keyed to maps. Some people may wish the entries were longer, but that just underscores the economic differences between Web publishing and book publishing. And some readers may be concerned at the lack of scholarly content. But that’s to miss the point of the book (and the Web site) entirely. Mr. Walsh isn’t a scholar. I don’t think he’d like having the job of researching and writing designation reports for the Landmarks Preservation Commission, for example. His urban epistemology is both different from and complementary to landmarks research.

As Mr. Walsh writes in his introduction:

“Despite New York’s insistence on renewing and reinventing itself every few years, thankfully there are examples of things left behind, or perhaps clandestinely left in place, that provide clues as to what was there before. Maybe it’s a street sign that the MTA has neglected to replace; a rusty cast-iron lamppost on a side street; an advertisement painted on a building for an obsolete product; or a sign in a subway station directing you to a street that has been renamed.”

Mr. Walsh grew up in Bay Ridge, Brooklyn, where he accompanied his parents and grandmother on wide-eyed walks and bus rides through the streets of Bay Ridge and Borough Park, learning as a child not merely to see but to notice. He also experienced, at the age of 7, the destruction of a whole part of Bay Ridge when the Verrazano-Narrows Bridge was built by Robert Moses. That taught him a lot about urban loss. Early on, his course was set. He got the idea for his Web site in 1998. With camera and notepad, he began his explorations and documentations — always on foot or by bike, never by car.

The book has 627 entries with titles like “The Desolation of West Street” and “That Thing at Ocean Parkway and Avenue U.” The former is about West Street in Greenpoint, Brooklyn: “West Street is lined on both sides by sidewalks composed of wooden blocks. As far as I know, NYC has no other remaining wooden-blocked sidewalks.” As far as he knows! In fact, I’d venture that no one in city government could answer that question. And, as few others have trod over so much of the city’s turf as Mr. Walsh, I take him as authoritative when it comes to stuff like that. And what is that thing on Ocean Parkway, anyway? “It’s big, it’s ornate, it’s rusting, and I hadn’t a clue what it might be.”Turns out it’s an air vent for the sewage pumping station beneath that intersection. It’s a city of true spirit, pride in itself, and dynamism that once built its sewage-pump air-vents with graceful ornaments to make a visual virtue of something so utilitarian.

And it’s a city of true spirit and pride in itself — a city worth getting to know — that can enrapture Kevin Walsh, who then enraptures us.