The Size dropdown tool contains icons for changing how many cells are visible in your viewport
User can make a 1×1, 2×2, and 3×3 viewport grid, with 1, 4 and 9 images - respectively. The 2×2 option is shown below:
When you click one of the options, the software will ask if you want to keep the current images or replace them.
The custom size option allows you select how many cells tall and wide you want your viewport to be.