In the 20th century, urban observers like Jane Jacobs praised the interactive sensory and social experiences that lie on any good block in Greenwich Village or Back Bay Boston. They cited 19th-century precedent, admiring humanely scaled buildings with their wealth of detail and texture, overlaid with the modern era’s democratically raucous street life. Discovering worthwhile contemporary examples of urban vitality, however, has often meant traveling outside the U.S. After a 13-hour flight to Japan, one can find age-old civic traditions mingling with tomorrow’s, out on the open street.

The first, most obvious lesson—one already familiar to Western audiences—is apparent on any Japanese byway: Low-rise, high-density cities can make humane places to live. The civilized residential heart of Tokyo beats outside the governmental core, a hop away by commuter rail. There, unnamed roads conform with the topography, combining four stories of housing above the odors and colors of streetside shops: fishmonger, pharmacy, sweets, antiques, cheap clothing, hardware repair, flower vendor. From wall to wall, a constantly rolling tangle of baby strollers, conversation, and the errant auto converge in a quotidian version of street-heaven.

Conversely, in a city of 8 million people where not everyone can live downtown, transportation counts. Subways link the metropolitan area, interconnected to larger rail lines, buses, and planes, yet a daily commute may take 21¼2 tedious hours from the eastern suburbs. Despite a plethora of rail, including accurate-to-the-moment bullet trains and private lines, freeways can be jammed with Toyotas and Hondas, and at certain hours, the sidewalks seem impassable. Everyone wants to be near the gravitational core.

Unlike Western cities, which owe their rationally gridded roads to the Roman military camp, Japan’s urban origins are more complex. In this multilayered country, mountain wilderness rolls down to space-age cities like Osaka or Tokyo, which, in their historic antecedents such as Kyoto, constantly unfolded inwardly, as wrapping became artful for objects and people (think of the kimono, with its under and outer garments). The late-20th-century reconstruction boom brought astonishing modernity and a stylistic polyglot to the entire country, with a certain grimy urban aspect. Much as John Portman envisioned in this country, layers translate into levels where land is scarce: In Osaka, skybridges connect tall structures; in Tokyo, shopping and dining regularly occur below grade. Despite the presence of a few well-visited parks and the Imperial Palace grounds, only a few large open spaces allow breathing room. The street represents Japan’s contemporary face, the visible, animated component of the whole organism.

Jump downtown to the contemporary drag, where Sunday evening activity reaches fever pitch on the Ginza—blue and red and white signs vertically ablaze and all doors open. Despite Japan’s current, larger economic doldrums, no slowdown in retail activity seems apparent. Stylish shoppers four abreast buzz through the Matsuya department store or the new Hermes emporium, its oversize glass-block facade designed by Renzo Piano. The brand matters, whether the brand is a famous architect or a silk scarf.

And what do you do on a street? Move. You walk, ride, pause, and then walk again, taking the measure of time and place in one meter increments, the width of the human stride. Outdoors in Tokyo or Milan or New York, we fully engage life, not passively but by moving and seeing, watching, gabbing on cell phones, eating, and occasionally buying. But to see this urban vitality as simply the visible heat and light of commerce misses part of the point.

What I saw in Tokyo has more to do with a kind of human unfolding for people whose lives are circumscribed by other physical and social layers. On the street, we put on a new set of garments, what the 17th century would have termed raiment—comprising an environment for mind and body that is broader, open to the sky, electrified with color and the hum of the present. In 21st-century Japan, as in 19th-century New York, we are drawn inevitably to the light, and it shines most clearly on the street. The old lessons about urban life still apply, translated and plugged into a new age.