The positive space in an image is basically the space occupied by the subject. It is on this area of a composition that photographers tend to concentrate their attention. It is also the area of an image that a photographer hopes the viewer will focus. The space surrounding the subject, maybe the sea or the sky, is known as the negative space and generally attracts less attention. Negative space is the space between the positive space and the frame.
If a subject fills the frame, there is no negative space but the subject may become overwhelming and unreal because the viewer cannot understand the context in which the subject was seen. If the subject fills most of the frame there are only small areas of negative space and the result may still be unattractive. Ideally, the positive space should provide the centre of interest in the image, and the surrounding negative space will be designed to draw or lead the eye to the subject.