Michael Sorkin is an American architect, a professor of architecture at City College in New York and easily one of the best architecture critics around. His collection of Village Voice columns, Exquisite Corpse (a title taken from the surrealists), which was published in 1991, confirmed Robert Hughes's opinion that "he is unique in America  brave, principled, highly informed and fiercely funny".

With All Over the Map, a collection of articles from the Architectural Record, Sorkin continues to focus on New York but, as ever, his critical thinking has wider implications. His pieces often start with an arresting, polemical opening ("All architecture is political"), to be followed by a tangential wander around a topic before a more focused two-paragraph summation and an equally strong final sentence ("The only answer to terror is an excess of democracy", "Good cities are a bulwark"). Sorkin is a flâneur with a sense of public purpose.

The book begins in 2001 with the destruction of the World Trade Center and ends with his own architectural manifesto  one that owes a great debt to Jane Jacobs, author of The Death and Life of Great American Cities. He argues for sustainable, bounded, polycentric and diverse cities, and is most interested, as someone who has long specialised in city planning, on "work at a scale that can genuinely be judged for its public arrangements and effects" rather than on individual buildings.

Sorkin argues convincingly that the Ground Zero site in Lower Manhtattan should be open, public space that encourages "peaceable assembly" (with its first amendment echoes) as its most important activity  something in short supply there. (He is horrified that Manhattan has become the world's largest gated community.) He rails against Larry Silverstein, the "philistine leaseholder", and the Lower Manhattan Development Corporation. When Daniel Libeskind, who is now masterplanning the site, first produced his design for the so-called Freedom Tower, Sorkin wrote that "with its bellicose iconography of strength, its giganticism, and its emphasis on heroism  [it] seems to commemorate victory". The One World Trade Center tower, Skidmore, Owings & Merrill's skyscraper, is due to open in 2013: Sorkin's criticism still pertains.

He is undistracted by the false debate about which was the best design in the Ground Zero competition, questioning the very idea that there must be buildings to replace those lost and looking at the wider context of the ecology of Lower Manhattan and beyond. "We do not hallow this ground simply by filling it with buildings," he writes. It is "disaster triumphalised", and he asks "why must the world's tallest office building be built on this hallowed ground?" He dismisses Libeskind's "treacly recitations of his immigrant sagas" and is disgusted by a fashion piece that compares the eyewear of the design competition finalists. "Never was vision so conflated with sight or sore eyes," he writes scathingly.

All Over the Map seeks to redress what Sorkin calls the "crisis in the public realm" from "car bombs in Kabul to CCTV cameras in London, from defensive 'street furniture' in Manhattan to the rampant privatisation of everything" and especially urban sprawl. I'm not so sure that sprawl is, as he claims, America's special contribution to urbanism, but it's easy to agree with his ringing conclusion: "Sprawl is unsustainable. Cities are the cure."

Sorkin doesn't pull punches  he writes a devastating obituary of architect Philip Johnson, a bête noire, whose body of work is merely "mediocre" and who was "clarifyingly emblematic of everything revolting about architectural culture, from his long love of the Nazis and his unspeakable anti-semitism, to his club-house conduct of architectural patronage ... his fey irony, his upper-crust superficiality ... Basta! Good riddance!".

He laments the decline in the standards of the architect Rem Koolhaas, demonstrated especially in his Prada buildings  how "Rem becomes Rem©", as he puts it. Koolhaas's non-committal view of the city, he argues, is often nothing more than "a series of laminations that serve its shopping subjects by smoothing the flow of traffic". (Though perhaps Sorkin shouldn't shout too loudly about these capitulations to the market  his own studio's Seven Star Hotel project in Tianjin, China, appears little different.) A chapter entitled "Entering the Building" is an Orwellian satirical riff on security, crowning Sorkin's belief that "we are moving toward a national security city, with its architecture of manufactured fear". The final directive is a bitter "Have a nice day."

Sorkin repeatedly urges us not to be blinded by form. "Halliburton headquarters (or Saddam's palazzi) may be gorgeous," he writes, "but that isn't exactly the point." As he says in a chapter entitled "Advice to Critics", "Style ... often conceals more than it expresses." His most important admonition, however, is never to be "a conduit for someone else's delusions"  something no one could ever accuse him of being.

Michael Sorkin has long been America's most invigorating writer on architecture. His preferred medium is the medium-sized article, journalistic not academic, and his standpoint that of an enraged but forever hopeful liberal, rooted in the dense, diverse streets of lower Manhattan. His targets are the corporate powers that, as he sees it, would crush the freedoms that make cities  especially his own  what they are. Also, or more so, the architects who go along with such powers, and obligingly ornament their monuments and instruments with distracting shapes. Also the critics who applaud the architects who dress the works that crush the freedoms.

All Over the Map is a collection of his writings from the first decade of this century, and several pieces reveal his fine line in satirical contempt and bleak humour. In "Entering the Building", he riffs a 62-point hallucination of security measures gone mad  "allow the Sniffer-Dog (green camouflage uniform) to sniff you wherever he or she pleases"  which, needless to say, is not so far from a possible reality.

The antihero who helps Sorkin to define himself is the late Philip Johnson, the godfather (in the Marlon Brando sense) of American architecture from the 1930s until his death aged 98 in 2005. Early in his career Sorkin outed Johnson as a committed Nazi sympathiser considerably less repentant than he ought to be, as well as a cynical player of power games, which latter characteristic Johnson himself did not try too hard to hide.

There is a note of regret when Johnson's death, in the time span of this book, obliges him to write "My Last Philippic". Except it isn't: Philip Roth's novel The Plot Against America, in which Charles Lindbergh becomes a pro-Nazi president in 1940, inspires Sorkin to imagine Johnson embracing the regime, and designing for it remote themed towns for black people and Jews. The features of "New Plantation, Alabama", privately called "Coontown" by Johnson, included the "'Tar Baby Caryatids' which held up the front porch of 'De Gen'ral Sto' on Main Street".

Sorkin's first book of essays, Exquisite Corpse, appeared 20 years ago, and as he now wryly notes: "My introduction bid a stirring farewell to critical writing, promising that I'd devote myself exclusively to architectural practice henceforth." He couldn't stay away, but his pursuit of work as an architect makes his latest book more complicated. Exquisite Corpse had the greater clarity and certainty of someone less enmeshed. In All Over the Map he struggles with the compromises that go with trying to get work from the same political-economic complex that he likes to attack. He flies a lot, which is not very ecological, and accepts commissions in China, which is not a very liberal place.

He can also be a lot less fun and agile when he tries to say what he thinks is good architecture. In praising one of his heroes he talks of "closely identifying the prosody of detail and organisation of building to clear social and environmental agendas". There must be a better way of saying it. For readers unversed in current architectural jargon, appreciation of this book requires some judicious skipping over the muddier parts.

His own designs, featured in the book as drawings rather than completed buildings, don't completely convince that they will unlock the answers to the social issues he raises. He is too much in love with form, favouring grandiose, quasi-natural shapes, like rock formations. There seems no guarantee that they would not end up as the same gross sculptures that you get in Dubai, and which Sorkin excoriates.

The most persistent theme is the architectural response to the 9/11 attacks on the World Trade Centre, which happened in Sorkin's neighbourhood, early in the time span of All Over the Map. He combines his usual astute analysis of the politics with his own ideas of what might be built there  "A World Peace Dome" for example. These, it seems to me, contribute to the extremity of the debate that took place at Ground Zero, between vision and commerce, which helped make it inevitable that commerce would win.

Then again, he comes up with real eloquence and precision in defending his dearest subject, the importance of true, uncompromised public space. He defines essential freedoms  of assembly, access, and of "use and expression"  together with the importance of the "stimulating accident". This pretty much nails what we want from the open places of our cities.