The idea in one line. A shop floor is a ranked argument, not a decoration. Every metre and every fixture is rented from the business at a price, and the merchandise on it must pay that rent in sales.
Two numbers. SALES DENSITY = sales ÷ selling area (per square metre, per week or per year). LINEAR PRODUCTIVITY = sales ÷ metre of fixture or rail. Density judges the store; linear productivity judges the fixture and the category on it. A rail at half the store's average is a subsidy paid by the rails that beat it.
The floor has a geography. The first three metres — the decompression zone — where the customer does not see product yet; she is adjusting. The right-hand turn and the power wall — the first place she looks: hero and fashion roles live here, not core. Eye level, the strike zone (roughly 120–160 cm) — the most productive shelf. Hot zones: entrance sightlines, ends of runs, the path to the fitting room and the till. Cold zones: corners, low shelves, behind pillars. Adjacency: what sits next to what makes the second purchase easy or impossible.
Why it matters. Space is the one merchandising input that cannot be reordered. A range that fits the plan on paper may not fit the floor; a floor that looks beautiful may hide the best sellers at ankle height. Productivity by fixture is the only honest way to argue about layout: "it looks better there" loses to "€1,200 per linear metre".
The trap. Rewarding image with prime space and starving core. The window earns the visit; the core earns the rent. Both need their place, and the numbers decide the split.
The bridge. Signal strength from your trend work sets how much space a fashion story deserves: an accelerating signal with independent carriers can hold a power wall; a fad holds a table for four weeks.
Practice. In any store, walk the floor with a notebook: mark the first fixture you saw, the eye-level products, the corners. Then ask a staff member what sells best — and check whether it lives where you looked first. The gap between the two is the store's cost of space.