How patterns tile

When designing patterns, it helps to understand how Adobe Illustrator tiles patterns:

• Patterns tile from left to right from the ruler origin (by default, the bottom of the artwork) to the top of the artwork. Typically, only one tile makes up a fill pattern. Brush patterns can consist of up to five tiles--for the sides, outer corners, inner corners, and the beginning and end of the path. The additional corner tiles enable brush patterns to flow smoothly at corners.
• Fill patterns tile perpendicular to the x axis. In contrast, brush patterns tile perpendicular to the path (with the top of the pattern tile always facing outward). Also, corner tiles rotate 90 degrees clockwise each time the path changes direction.
• Fill and brush patterns also tile differently in relation to the pattern bounding box--an unfilled and unstroked rectangle backmost in the artwork. For fill patterns, the bounding box acts as a mask; fill patterns tile only the artwork within the pattern's bounding box. In contrast, brush patterns tile artwork within the bounding box and protruding from or grouped with it.