The Italian term “andamento” (plural is andamenti) refers to the flow of the mosaic pieces, called “tesserae.” That is, the individual pieces of a mosaic follow the form of the image that is described. The Romans and Greeks invented this way of making images visually coherent in mosaics.
So for a landscape the tesserae will describe the arc of a hill down to the sea. But the sea will have tesserae that are parallel to the horizon--with an up and down flow showing the undulations of the water, and maybe curls for waves.
This classical way of creating a mosaic is much more time consuming than what I call “a tile job” wherein the shapes of the images are cut from squares of mosaic tile adhered to a backing. Thus this tile job will have a head of a person that is like a brick wall, rather than tile pieces curving around the shape of the head and the various facial features.