"(500) Days of Summer" is a movie about obsessions -- gentle, often charming and non-stalkerish obsessions, for the most part, but obsessions all the same. Chief among them -- after romantic love, the subject that stands always at the heart of the story, its existence always up for impassioned, practically theological debate -- is architecture.

The movie, set in downtown Los Angeles, is filled with shots that make the neighborhood look like an architectural guidebook come to celluloid life, mostly because Tom, an aspiring architect with a day job writing copy for greeting cards, relies on walking tours as a central part of his sometimes bumbling courtship of Summer, a flightily charismatic co-worker. Tom is particularly fond of the 1927 Fine Arts Building, on 7th Street, and 1902's Continental Building on Spring, which he proudly cites as downtown's first skyscraper.

It is surely significant that directors are now content to let downtown, so long a cinematic stand-in, play itself and even to put the neighborhood at the center of their story lines. There's a twist, though, to the picture's emphasis on architecture: It has been carefully edited to excise virtually all shots of buildings finished after about 1950. Don't expect to see Frank Gehry's shimmering Walt Disney Concert Hall or the Department of Water and Power by A.C Martin. Or Thom Mayne's Caltrans District 7 Headquarters, whose imposing, perforated-metal façade has made it a movie and car-commercial staple. Or Rafael Moneo's Cathedral of Our Lady of the Angels. Or even what was known until a year ago as the ImaginAsian theater on Main Street, an all-white curving design by Hodgetts + Fung that Summer and Tom might plausibly have visited for a matinee showing of some appropriately obscure Korean or Taiwanese movie.

The only time contemporary architecture figures in the story, in fact, is when Tom, sitting on a bench with Summer in Angel's Knoll Park, complains about all the parking garages that have recently disfigured downtown's handsome prewar profile. It's as if there are two kinds of buildings downtown: old ones full of character and new ones filled with cars. His view from the bench, in fact, pretty neatly sums up the movie's view of architecture: What he sees is a tiny, carefully trimmed slice of downtown masquerading as a panorama.

There are a few obvious reasons for that highly selective perspective. For starters, Tom (Joseph Gordon-Leavitt) and Summer (Zooey Deschanel) are both characters drawn to the old, quirky and overlooked: Neither one much likes new movies, music or fashion. Their taste, finely honed and fiercely held, is best described as anachronistic, both specific and wide enough to include "The Graduate," Regina Spektor and the Smiths. Then there's the fact that the movie's structure is itself retrospective: In aggressively shuffling the story line, the screenwriters, Scott Neustadter and Michael H. Weber, give us the end of the relationship early on and let us spend the rest of the movie looking back. The buildings on view fit neatly into that structure: The content of the movie is what's come before.

But there's another element of the picture's thematic use of architecture that says something intriguing about the relationship between design and certain quarters of American culture, particularly its twenty- and thirtysomething culture. "500 Days" is, as far as genres go, a hybrid picture, something of an emo version of a romantic comedy: It disdains machismo, futurism, violence and volume in favor of subtlety and heartfelt, if often mumbled, emotion.

The one time Tom really runs afoul of Summer's feelings is when he throws a punch at a guy who's been hassling her at a bar (downtown's highly photogenic Broadway Bar, by the way). Tom is one of a number of emo leading men to emerge from Hollywood this year, joining sensitive types in "Adventureland" and "Away We Go," among other pictures. As Gawker noted this week, the cineplex has been full of "gentle, sensitive, geeky male outsiders with a love of Lou Reed and snug hoodies."

With its very particular aesthetic point of view and calibrated tone, "(500) Days" shares much cultural ground not just with indie bands but with emo culture broadly defined -- with journals like McSweeney's (whose founder, Dave Eggers, cowrote "Away We Go"), radio programs like "This American Life" (whose host, Ira Glass, is Tom with chunky black glasses and a decade or two older) and so on.

Tom's architectural drawings, when he gets around to making them, are certainly not done with the aid of any computer software: They are eccentrically, minutely detailed throwbacks that he executes in a notebook, on a chalkboard at home or on Summer's forearm. No blobs or parametric wonders for him, thank you very much, nor any of the straight, spare lines of the International Style: His sketches are a cross between the charcoal drawings of Hugh Ferriss and the precise ink illustrations of McSweeney's favorite Chris Ware.

When the members of America's emo tribe happen also to be fans of architecture, they tend to like their buildings the same way they like their corduroys and their comic books (excuse me, their graphic novels): well-worn or obscure enough in terms of design pedigree to maintain a full measure of indie street cred. When the writer Sarah Vowell produced a video piece for the website of the New York Times three years ago on architecture, it centered on her love for the elaborately ornamented Chicago buildings of Louis Sullivan, who died during the Coolidge administration.

Tom and Summer try their best to find architectural relatives of the Chicago School in downtown Los Angeles: soot-stained but broad-shouldered and highly decorated mid-rise buildings like the Eastern Columbia, in particular. For them, the neighborhood's charm is decidedly romantic, and therefore never far from nostalgia, and the buildings that sum up its appeal are underrated architectural gems that have managed through all these decades to avoid the wrecking ball. And yet as was the case in last year's "In Search of a Midnight Kiss," an inferior movie but one with many scenes downtown, the characters in "(500) Days" symbolize a younger generation of Angelenos who find the neighborhood appealing precisely because it feels to them dusty and underappreciated, rather than notable for new buildings by some of the world's leading architects.

Another way, maybe, to say the same thing is to point out that emo culture has produced plenty of music and other expressions of contemporary angst and feeling but precisely no contemporary architecture. (Where is architecture's Vowell or Conor Oberst, its Michael Cera or Adrian Tomine?) Maybe we need just to wait until designers in their 20s mature and make it big, but any architecture student with taste and a worldview like Tom's would find himself entirely out of step with present-day architectural discourse, particularly as found these days at the university level, where the choice is mostly between liquid, cutting-edge digital design or the dregs of the opaque Continental theory celebrated for much of the 1990s. Still out of fashion, for example, is the interest in proudly historically minded design that helped propel the postmodern movement two or three decades ago.

There is a burgeoning group of young architects newly interested in ornament and decoration, but their version is highly digitized and futuristic. And if there are two words we can say for sure that hold little interest or meaning for Tom and Summer, "digitized" and "futuristic" would have to rank near the top of the list.

For that reason, it's hard not to feel a little sorry for Tom as he interviews for a job at an architecture firm -- located in the 1893 Bradbury Building, naturally -- near the end of the movie. He seems to have plenty of rejection, or at least professional alienation, in store if he's really set on pursuing a career in contemporary architecture. Maybe the L.A. Conservancy is hiring.

christopher.hawthorne @latimes.com