The board outline is a closed figure that constrains the board shape. It determines the area available for placing components and routing connections. When you create a new 2D PCB, by default a rectangular outline is used. The board outline defines the exterior dimensions of the PCB. When you first create a PCB, a default board outline is created. You can draw a different board outline in the 2D PCB or 3D PCB spaces, according to your needs.
Fusion electronics detects properly drawn contours (single closed outline, non self-intersecting) and shows the board area in a different background color compared to the rest of the background. This geometry is drawn in the 20 – Board Outline layer. The board outline also includes mounting holes and milling contours, drawn in the 46 - Milling layer.
If you delete the existing board outline, the components and airwires remain in place, but the gray board surface fills the entire drawing canvas. When you create a closed figure for the new board shape, the gray board surface will be constrained to the interior of the board shape.
If you are creating a new board shape considerably larger than the old board, you can create a new shape that entirely surrounds the old board, then delete the old board.
The Board Outline in the 3D PCB is contained inside the Outline Sketch.
If you use the Project tool to reference geometries from the Assembly Context, the Board Outline can consume updates from the mechanical enclosure.
If you select a profile other than the one in the Outline Sketch using the Define Board tool, the outline sketch will not be used to define the 2D PCB board outline.
If you modify the 3D board shape and push the changes back to the 2D PCB, from then on the board shape can only be modified via the 3D board outline sketch.