Petri Artturi Asikainen would regularly accost strangers in Tokyo, on the streets, in parks or bars and on trains. With a high-end Nikon D3 digital SLR in his hands, the lanky and bespectacled Finn would ask — somewhat timidly summoning one of the few Japanese phrases he had memorized: “Can I take a picture of you?” If the answer was in the affirmative, he’d then fire off another, even more personal inquiry: “How old are you?”

On and off, the freelance photographer kept on making such rather sudden contact with Tokyoites, day and night, for about three years. In all, he reckons he approached around 2,500 people — and succeeded in taking pictures of nearly 500 of them.

Finally, in 2012, he put together a series of 202 portraits — presented as 101 man-and-woman pairs — of people in the city aged right the way through from newborns to centenarians. And, in December last year, the fruits of his three-year project revealing an amazing diversity of life in this city of some 13 million people finally became available in a photobook titled “100 Years in Tokyo.”

For Asikainen, who has worked as a freelancer for 20 years, shooting mostly for magazines and corporate publications, this was his first long-term personal project — and one he says he greatly enjoyed.

“I wanted to do some (extended) project, then I wanted to do something in Tokyo,” he said at a cafe in Minato Ward last week, noting that he had been struck by the city’s “visual abundance” ever since he first visited as a tourist in 2005. In fact, in the foreword of his 216-page book, penned in Finnish, English and Japanese, he sums up the city, saying: “It feels familiar like any Western metropolis, yet completely strange and different.”

Asikainen, who lives in Shibuya Ward, said that when he embarked on the project in 2009, he didn’t know whether his idea of photographing people across such a diverse range of ages would really be possible, and he admits he has chosen his subjects “more or less randomly.”

“Somebody who knows the (Japanese) culture very well told me in the beginning, ‘You’re never going to make it. Japanese are far too shy for that,’ ” he said. “But I was surprised to find it was easier than I’d thought.”

He attributes the success of his project partly to the city’s renowned safety, saying he never felt threatened approaching strangers anywhere in Tokyo at any time of the day.

So, from the neon-lit streets of Shinjuku to the so-called oldies hip mecca of Sugamo, known for its small shops selling quaint clothes and knickknacks, to the upscale Ginza shopping and business district, Asikainen never hesitated to cover an astonishing variety of locations.

In the process, he captured images of a similarly astonishing range of people, including students, shopkeepers, business types, old residents of nursing homes, a cyclist, a roadworks laborer and even a homeless man lying on the ground. Through introductions, he was also able to picture some people in arranged settings such as in their homes and at their offices. The book even features a handful of people he got to know in the course of daily life, including 33-year-old Minami Aoki, who works in the shop in Nakano Ward where he bought his first bike in this country, and Yoko Toyama, 23, a real estate agent in Gotanda, where he signed the contract for his rented apartment.

Interestingly, too, although Asikainen took most of the portraits within minutes of meeting people who had little or no relation to one another, when the results are reviewed between the covers of a book, they start to assume a quality greater than the sum of the parts.

Indeed, just browsing those pages feels akin to being shown a slideshow depicting the course of a Tokyoite’s life, witnessing how a baby with its adorable newborn freshness grows, through vulnerable and turbulent teenage years, into the prime of life which morphs into increasing old age.

One interesting skill Asikainen says he has acquired along the way is the ability to guess the ages of Japanese people accurately. “The funny thing is, for Western people, it’s difficult to tell someone’s age here because Japanese people look much younger than they are,” he observes. “But then, when I was doing it I got very good at it. Actually, when I needed, say, someone aged 56, I very seldom missed by more than two years.”

Feeling an irresistable desire to test his newfound ability, I asked him to guess my age, stressing that I didn’t need any gesture of politeness from him. I asked for a brutally honest assessment of how old I looked — something I must say I’m reluctant to ask anyone at all these days.

“Hmm … ” he mused — then opted for a number that was five years shy of my true vintage.

I rejoiced with excitement, though Asikainen looked as if he had just lost a game of poker. Then he burst out laughing. “I don’t get it any more — I’ve lost it,” he announced, seemingly crestfallen.

As well, he confesses, with “100 Years in Tokyo” now in bookstores, he’s at something of a loose end as he scouts around for another fun and thought-provoking project to tackle.

At present, he says, he is toying with the idea of searching out and photographing all kinds of “niche businesses” that could only survive in a city like Tokyo, where the daily influx of workers from the suburbs rockets the population to some 36 million.

“That means there can be, for example, services or shops targeting very specific groups of people,” he notes. “And in a city this size, I guess it’s possible to focus on relatively small groups of people. If you take one person from 1,000, it’s still a group of 36,000 in Tokyo.”

“100 Years in Tokyo” (Aalto Arts Books, ¥3,675) is available in Tokyo at Aoyama Book Center stores, the Junkudo Ikebukuro store and others. A flip-through video of the book can be viewed at pa.artturi.com/books. For more information, contact books@artturi.com.