"How can money be the root of all evil, when shopping is the cure for all sadness..." Elizabeth Taylor
Effective merchandising demands the most effective use of available retail space, ultimately seeking to capture the impulse of the customer to buy more and to buy better. An understanding of customer behaviour in the shop, often learned through trial + error and observation can be used as a positive sales tool.
It is telling that large retailers employ policies of shop layout, based upon research and understanding of consumers' purchasing patterns.
An initial consideration is a basic building floor plan, and every shop through it's physical layout will have areas which draw higher traffic, as well as areas of the shop which may not be explored so much for reasons such as congestion (perceived or real) or simply being at a distance from the point of entry.