The ArtStation mosaic provides a randomized selection of artworks liked by the community. It helps artists to get more exposure and for new visitors to see the range of work by the ArtStation community. There is no special selection process or way to get onto this wall. It is entirely randomly generated.
The way artworks are displayed is randomized - Within a set of images that show up, the ones with the most likes show as larger squares but there is no special order that determines the placement of artwork.