How to export only the viewport in aftereffects?

Question

I'm experienced with illustrator though very new to after effects and having big trouble with the most basic of things.

What I'm trying to do is that basically I have a huge HD map and I want to show a path in part of this map. I've succesfully got it scrolling just where I want it in the viewport that I see, however when I export the entire map is exported, not just the section I was zoomed into.

The question is, how do you extract only part of an image in after effects with the rest being considered out of bounds?

In doing this I don't actually want to reduce the image resolution and the rest still has to 'exist' as the path will scroll there.

Answer 1

Precompose the map layers, then in your Main composition scale up the Precomposition to show what you want exported (and keyframe Position if that's what you are doing to keep the path in view). Your Main composition only needs to be the size of the exported video - not the size of the HD Map (the Precomposition should be the size of the HD Map).