VANCOUVER – Most people see height. Ian Clark looks for length.

Clark is the Vancouver Canucks’ goaltending professor. He was the goalie coach who helped Roberto Luongo elevate his game when he came to Vancouver, then built Sergei Bobrovsky into a Vezina Trophy-winner when Clark went to Columbus.

In his first National Hockey League season back on the Canucks’ staff, Clark is helping starter Jacob Markstrom play the best goal of his life. But his masterpiece could one day be Thatcher Demko, the tremendous goaltending prospect from the minors who, since his call-up to the NHL on Jan. 4, has been taking a heavy course load at Clarkie U.

The 23-year-old from San Diego is six-foot-four. That’s not what Ian Clark sees.

“I always measure goaltenders from an anatomical-athletic perspective on length,” Clark told Sportsnet before Demko and the Canucks got a rest day on Monday.

“Length is the key thing, not so much size. You can have a six-foot-four goaltender who lacks athleticism and he can’t lengthen himself (to make saves). But if you watch Andrei Vasilevskiy play (for Tampa), you’re amazed when you watch his length. And then he combines that with good structure and intelligent play. So he’s making simple saves simply and then out of nowhere, his leg comes out and that’s the length that he has.

“In Thatcher’s case, for me the question is: Anatomically, working with that athletic ability, does he have length? He’s a long goalie and that is something that’s very promising.”

Length is what allows goalies to extend, to reach or even contort to get to pucks. Height is little good if the goalie is not athletic enough or in the proper position to enable length.

When Markstrom appeared beaten on a rebound on Sunday but instead thrust his left arm out and back to snare Florida Panther Nick Bjugstad’s point-blank shot during the Canucks’ 5-1 win, that was length.

But even length doesn’t matter if the goalkeeper lacks the mental pace to read and anticipate puck movement at the NHL level.

“If we’re chasing the game all the time, we’re too physical and will always have a tough time making those reads,” Clark said. “With all the offensive activity in the National Hockey League today – lower save percentage, more goals, more creativity, active D – the ability to have our eyes working for us is essential.”

And that is why Canuck practices, seemingly endless for Demko at the moment since there’s no indication when head coach Travis Green will actually start him in a game, are vitally important to the 2014 second-round pick as he transitions to the NHL.

Vancouver traded backup Anders Nilsson two weeks ago not so Demko could come up from the Utica Comets and try to lead the Canucks, but so he could train with Clark and work on the foundation the team hopes will eventually make him a No. 1 goalie in the NHL.

“It’s a big adjustment,” Demko said. “The guys are moving quicker, shots are coming quicker and plays develop quicker as well. You definitely have to read the game quicker.

“I just want to become acclimated as quickly as I can. It will come in time and with playing games and all that good stuff. But these practices are huge for me, just to see the shots and the pace and how strong guys are in front of me. So just keep getting acclimated and build confidence and get comfortable as the season goes along.”

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Demko first worked with Clark at training camp in September. When he suffered a concussion and was returned to Utica to start a third season in the American Hockey League, Demko travelled with what Clark described as a “laundry list” of things he needed to improve.

That could be humbling, even a little insulting, to a player who had a brilliant college career at Boston College and was an AHL star last season when Demko posted a .922 save rate with the Comets. But Demko accepted Clark’s recommendations.

“I haven’t been with Thatcher a lot, obviously,” Clark said. “What I can tell you is he spent his time down in Utica very well. He left with sort of a laundry list of things to think about and begin to develop, and I can tell you he has checked off a number of those things, which is great for the franchise.

“Yeah, there’s some things Thatcher needs to develop. But my point is, he took it upon himself to use that time (in Utica) productively. He took things upon himself, which is the sign of a mature goaltender.”

Demko said: “One thing Clarkie is really good at is putting everything into terms. The way he looks at the game is a little different, but in a good way. When the communication is there and everyone is on the same page, the player is going to have a better chance to develop successfully. When you can narrow it down to maybe five things that you can work on instead of trying to look at the big picture … that can be overwhelming sometimes. That list that Clarkie gave me I thought was pretty helpful.”

Clark said he tells his goalies that they’re in charge of their development, and he is just there to assist.

“I’m more of a compass than a GPS system for them,” he said.

He’ll point them the right way, but the player has to get to the final destination on his own.

Demko desperately wants to get there. He badly wants to play, too, but knows a game or two in January isn’t his destination.

“This is what I’ve been working for,” he said. “I’ve got no right to come up and start demanding stuff. I’m just working hard every day and when they decide to give me a chance to play, I’ll be ready and be excited.”