How must the boundary be marked?

Under Law 19:

• The umpires decide the boundary of the field of play before the toss, and it's fixed for the whole match. No part of any sightscreen may be inside the field of play at any stage.
• Wherever practicable, mark it with a continuous white line or an object in contact with the ground (such as a rope or cushion).
• White line: the edge of the line nearest the pitch is the boundary. Flags, posts or boards used only to highlight the line must sit beyond it and aren't themselves the boundary.
• Object on the ground: the boundary is the edge of the grounded part of the object nearest the pitch.
• No continuous marking: flags, posts or boards can mark points, and the boundary is the imaginary straight line between the two nearest points.
• Any boundary that can't be identified in these ways is decided by the umpires before the toss. An obstacle inside the field (for example a tree) isn't a boundary unless the umpires decide so before the toss.
• If a solid boundary marker is disturbed, the boundary is treated as being in its original position. The marker goes back as soon as practicable (during play, as soon as the ball is dead), and any part of a fence or marker that has come inside the field of play is removed at the same point.

Crease markings (Law 7) are white lines; the bowling and popping creases are measured to the back edge of the marking and the return creases to the inside edge.