Adam Taylor By default, the trellising adds a chart for each item in the query. So if there are 10 countries in the horizontal trellis, you'll see 10 charts going across the screen. There are 2 items in the vertical trellis, then there will be 2 rows of charts going down the screen.

The option above is to OVERWRITE the default, and tell the visualization engine to limit the number of horizontal charts to 1,2,3 or 4 before wrapping to the next row. It effectively breaks the natural trellising of the element selections. If you set it to 4, you'll end up with 4 charts across and 5 rows down (4x5=20), instead of 10 across, by 2 down (10x2=20).