The S-shape strategy is also called the Traversal strategy. This strategy leads to a route in which the aisles, that are to be visited, are totally traversed. Aisles where nothing has to be picked are skipped. Thus aisles are visited in the shape of an S. The picker thus enters an aisle from one end and leaves the aisle from the other end, starting at the left side of the warehouse. After picking the last item, the order picker returns to the front end of the aisle. This strategy is used frequently, because it is very simple to use and to understand.
Below, you can see how the selected items are to be picked according to the S-shape heuristic in a warehouse with a central depot and no cross aisles. The order picker starts at the depot and then enters the left most aisle containing items or the right most aisle containing items, whichever is the closest. The picker goes from one item to another by crossing the (item containing) aisles entirely. Finally, he returns to the depot.