Why would I need to change the layout? Every time I upgrade the desktop for a new Ubuntu version it defaults it to a 2×2 layout.
I don’t have a monitor on top of another so why would I use vertical workspaces? It maybe has advantages for some else workflow. Not mine. I’m used to horizontal multiple screens.
How can I define a new workspace layout? You can change several parameters with the Compiz Config Settings Manager. I found that some friends didn’t have it installed. So, just install it first.