Purpose of board outline?

[miceuz]

Now while preparing a board I have hesitated - if I have an irregular shaped board, does outline (Dimension layer in eagle, Edge cuts layer in kicad) have to follow the insides of routing, i.e. deisgnating exactly where the edges of my irregulary shaped board are or does it have to be a rectangle enclosing whole PCB including routing paths?

What's the meaning of this layer anyway?

[Kohanbash]

Hi
The outline is usually what your final board should look like and how the PCB manufacturer should mill the edges.

So for an irregular board your outline would be that irregular shape.

[TommyGunn]

Often an assembler will need it to for the stencil. It helps the center a board if all the parts are close to one side.