It's not an easy question to answer. If it is merely how much space we take up in the universe, then it's pretty straight forward, but odds are, it's a whole lot more. It's how visible we are, how many resources we require, and perhaps most importantly, how easily we are able to hide. That's a big part of the philosophy that you get watching the beautiful animation On The Day You Were Born.
George is reclusive, and it's an annoyance to his sister.
As he's on the phone to her, he begins to grow. He continues to grow, and as he does so, his point of view changes, and he comes to understand... something.
That's the basic story. It's a body horror work, but a psychological body horror work. It's got a touch of Kafka, of Alice in Wonderland. The story is told two ways - through lovely animation that follows George, and through a lovely bit of narration handled by the incredibly Beth Grant (Donnie Darko, about 1,000 other films and TV shows you've seen) that doesn't dwell on the character, but instead drives things forward.
The growth has led George out of his comfort zone, but more importantly, it has forced him to experience himself in a new way, which makes him realise that there is something to him that is of interest. That's a big deal, but it's also only a thing that happens along a path, and that makes things fascinating.
You can see On The Days You Were Born as a part of Animated Worlds - https://payments.cinequest.org/websales/pages/info.aspx?evtinfo=85257~78899376-35a9-4153-8303-e1557be2dc32&epguid=d52499c1-3164-429f-b057-384dd7ec4b23&#.XGR2GlxKi70