The canvas is the white rectangle on your screen where you
are placing your object. You can place objects anywhere else and it is perfectly
legal, but canvas represents the part which will be exported so it defines
the size of the output image. (However you can export any other part of the
document with the Crop Tool).
CompactDraw doesn't ask you before you start your project for the canvas size. Instead default size will be used. This is done because many times you don't have to know the exact size before the project starts. CompactDraw uses smart reverse approach - to fit the canvas around the object when we are done. For that we have automatic commands Trim Canvas and Trim Canvas Expanded plus a manual Crop Canvas (All in menu Project). Thanks to them you don't have to worry about the placement of the objects on the Canvas. The Canvas can be resized to fit the objects. See the detailed description in Export.
However you can still use the first standard approach when you set the Canvas size before you start working. (For example if you need the project to be exactly 320x200 pixels etc..) - for that you have the Canvas Size and Color settings.
To change the Canvas Size and color:
From menu Project select Size and Color
To change the default Canvas size (which appear on start or
anytime you press New)
From Menu Project select General Settings
Note: In this case the current document doesn't change.