It starts with a small detail: a distinctive tree, an oddly shaped window or a passing streetcar.

After he’s scanned an episode of Degrassi Junior High for clues like these, Brian Donnelly heads to Google Street View and virtually walks the streets from one end of the city to another until he finds what he’s looking for.

Once he thinks he’s found a spot where a scene from Degrassi Junior High was filmed, he heads there by bike and photographs what it looks like today, posting the results on his blog, DegrassiPanthers.com.

Degrassi is still chugging ahead — the 13th season of its latest incarnation premieres Thursday, July 11, on MuchMusic — but Donnelly is going back in time. For the last two years, he’s been mapping every spot where Degrassi Junior High filmed its three seasons. In the process, he’s creating a record of how Toronto has changed in the last quarter-century.

“It’s a reference point for the city,” Donnelly says.

It’s also a detail-heavy task that’s turned into a downright mission, one Donnelly admits might sound odd for a 34-year-old man.

But it’s rekindled a love inside of him for Toronto, by sending him pedalling to pockets of the city he’s never seen before.

Donnelly was 8 when Degrassi Junior High premiered in 1987.

At first, Degrassi was a campy, funny thing to watch. But the characters grew on him, so much so that he named his first bike after character Melanie Brodie, because it was awkward and needed fixing a lot.

“When you watch Degrassi Junior High, it’s almost like looking at your own life. All those kids look pretty normal,” Donnelly says.

“Yick is a weird looking kid with big, thick glasses. Arthur is a pretty chubby kid and he’s not good at sports, but he tries. I was Arthur when I was in Grade 6.”

Donnelly’s quest to find every spot that appeared in the series started two years ago, after he bought a bike.

He called a friend and asked if he wanted to ride to Vincent Massey Public School in Etobicoke, where Degrassi Junior High was filmed.

“The game started out as, ‘Oh I know where this is, I know where that is. Let’s check if it’s still there.’ And then it became, ‘I wonder how many are still there.’”

Some places are gone, but not as many as you may think.

“What’s surprised me the most is how much it hasn’t changed,” Donnelly says.

One place that’s disappeared is Stephanie Kaye’s house, a spot Donnelly put a painstaking amount of effort into finding.

He had few clues. He knew the house number was 309 and it looked like it was on a quiet street that didn’t look as if it could be downtown. He could tell there was two-directional traffic.

Judging by the time of day — Wheels was wearing a jacket in the particular scene, so Donnelly deduced it filmed in the afternoon — and the shadows, he decided it was an east-west street.

That took him north on Google Street View and he finally found the building on Manor Rd. in the Davisville neighbourhood.

He biked kilometres each way to see it, only to realize Google Street View’s image is outdated.

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“It’s been completely flattened and rebuilt,” he says.

“Riding your bike up there to find nothing but disappointment at the end sucks.”

Stefan Brogren wishes he could remember some of these places more clearly.

He played Archie “Snake” Simpson in Degrassi Junior High and still plays the role in 2013, where Snake is now running Degrassi as principal. Brogren is also a director on the “new” Degrassi.

“There’s so many locations that, if I tried to find them, chances are they’re probably not even there anymore,” Brogren says.

“It’s hard for me even to remember where the junior high was because they used to take us there in vans from the main office, which was at Pape and Queen.”

Back then, Degrassi filmed all over the city, often at homes owned by people the cast and crew knew. A project like Donnelly’s wouldn’t be possible with the current Degrassi, which films on its own sets and rarely goes on location, Brogren says.

When he watches Degrassi Junior High episodes, he sees a city, pre-condo boom, that looks much sleepier.

But it’s more than the city and its buildings, he says, that look different in those episodes. It’s language and style, too.

“It’s a real time capsule for the city and for what teenage youth was in Canada,” Brogren says.

“As much as things change, a lot of things stay the same.”

Donnelly has two goals. The first is to finish his map of show locations.

The second is more personal.

“My goal is to have a beer with Snake (Brogren) and Joey (Pat Mastroianni) in the same spot they get caught drinking beer (with Wheels in Season 3).”