The Show Layer Boundary command enables and disables displaying the yellow dotted line that surrounds a layer in the image window. The dotted line is actually only visible when the layer is smaller than the image window. When the layer is the same size as the image window, the layer boundary is obscured by the image border.

Настройка по усмотрению для края слоя находится в диалоге Внешний вид окна изображения.