I've seen a page where they describe technology along with a Vocab to describe imagery data. It allows a client to zoom into very large images which are then tiled and loaded and set focal points to define what should be seen when minimizing the image. A little bit like the HTML picture element. I forgot the name of this page. Does anyone know what I mean?
Are you referring to Focal Point?
Focal Point: Pure HTML/CSS Adaptive Images Framework
A small set of CSS classnames to help keep images cropped on the focal point for responsive designs. Using only HTML/CSS, web authors can specify an image's focal point, which stays as the image's primary focus as the image scales on responsive webpages.
If this is not what you are looking for, they also link to related resources that might be of interest to you.