01 · Mechanics and boundaries
Mechanics and boundaries
A spaghetti diagram overlays an observed movement path on the physical layout. It can follow an operator, parcel, cart, or document, but one drawing should identify which entity is being followed. A parcel route and a picker route may differ substantially. The diagram reveals spatial relationships that a process flow chart hides, including backtracking and repeated trips to shared equipment.
Distance is a separate measure from duration. A short route through a congested doorway can take longer than a slightly longer unobstructed route. Carrying weight, reach height, safe access, and the direction of traffic also matter. The objective is a safer, simpler flow that supports the required work, not the shortest geometric line.
02 · Construct the analysis
Construct the analysis
Draw a scaled plan showing actual aisles, storage, benches, equipment, and permitted routes. Select a representative order family and observe a complete cycle. Number destinations in sequence and draw each movement along the path actually walked, not through shelves. Record purpose, distance, duration, carrying condition, and repeated trips. Use separate colors or separate drawings for entities and conditions.
Repeat observation across order sizes and busy periods. Summarize route segments in a distance table so the tangled picture has an auditable total. Ask why each trip exists before relocating equipment. A printer may be remote because of connectivity or safety; a supplies trip may indicate an absent replenishment rule rather than a poor location alone.
03 · Worked warehouse-dispatch example
Worked warehouse-dispatch example
The fictional North Quay warehouse dispatches a single parcel-order family. Its boundary starts when an order is accepted for release and ends at confirmed carrier handover. Demand is 240 orders in a 420-minute net working day. Each order contains three lines on average, but the example keeps the parcel order as the unit of flow. No number below describes a real organization or a demonstrated improvement. The purpose is to make the reasoning traceable rather than to present a success story.
A representative order spends 12 minutes awaiting release, 2 minutes being released, 18 minutes awaiting picking, 8 minutes being picked, 24 minutes awaiting packing, 5 minutes being packed, 10 minutes awaiting checking, 2 minutes being checked, 15 minutes awaiting loading, and 3 minutes being loaded. These mutually exclusive intervals total 99 minutes: 20 minutes of processing and 79 minutes of waiting. They describe one complete normal-route trace, not a statistically estimated mean for every order. A separate 100-order diagnostic sample contains 20 late orders, defined as handover more than 120 minutes after acceptance. The normal trace and late-order sample therefore answer different questions.
Three pickers, three packers, two checkers, and two loaders work in parallel within their respective stages. At the illustrated processing times, theoretical stage capacities are 157.5, 252, 420, and 280 orders per day. Picking is below the 240-order requirement even before interruptions or rework. Release has two staff and a theoretical capacity of 420. These capacities assume dedicated resources, identical order mix, and no overlapping assignments. They are not observed outputs and should never be reported as effective capacity.
One observed pick route travels 14 metres from release desk to cart, 26 to zone A, 18 to zone B, 22 to zone C, 30 to packing, and 10 back to the cart point: 120 metres total. At an illustrative unconstrained speed of 1.2 metres per second, walking alone would take 100 seconds, or 1.67 minutes. The eight-minute pick activity includes that movement plus searching, selecting, scanning, and handling.
A proposed route reduces distance to 84 metres, a 36-metre or 30% reduction. At the same assumed speed it saves only 30 seconds. If all other work remains unchanged, the illustrated pick time becomes 7.5 minutes, and three pickers offer 1,260/7.5=168 theoretical orders per day. The distance improvement is useful but still insufficient for 240 orders.
| Segment | Distance |
|---|---|
| Desk to cart | 14 m |
| Cart to A | 26 m |
| A to B | 18 m |
| B to C | 22 m |
| C to packing | 30 m |
| Return to cart | 10 m |
| Total | 120 m |
04 · Movement sequence
Movement sequence
05 · Interpretation and decisions
Interpretation and decisions
Interpret repeated crossings as an investigation signal. Check whether they reflect order sequence, storage policy, shared supplies, or queue avoidance. Confirm that a proposed layout leaves enough room for replenishment and emergency access. Test it with ordinary carts and the largest relevant parcels before treating the plan as feasible.
A weak application draws an ideal straight line between stations and claims the eliminated distance as saved time. A sound application traces the real route, measures the physical changes, and separately verifies any duration reduction. It distinguishes worker travel from material travel and accounts for the return leg.
06 · Sound application and adaptations
Sound application and adaptations
For many routes, use separate layers for product families or a frequency-weighted from-to matrix. Weight each route by how often it occurs, but retain rare hazardous movements even when their distance contribution is small. For congestion, timestamp entries to shared aisles and record stops; a static map alone cannot show simultaneous conflicts.
The diagram does not reveal digital handovers, capacity deficits, or value by itself. Pair it with time analysis and the process boundary. After a layout trial, repeat equivalent routes under comparable load rather than photographing a tidier arrangement. Check whether reduced walking increases bending, lifting, or interaction with moving equipment. The meaningful result is better flow with acceptable working conditions.
07 · Evidence and follow-through
Evidence and follow-through
Make the observation auditable before debating a countermeasure. Preserve an anonymous order identifier, acceptance and handover timestamps, route, line count, shift, exception flag, and the observer's definitions. A timestamp from a completed screen action may describe data entry rather than physical completion. Reconcile several records with direct observation and ask the person doing the work what each event actually means. Keep an uncertainty note when clocks differ or two actions overlap; rounding cannot repair an ambiguous boundary.
Observe ordinary work and exceptions over a period that includes opening, replenishment, breaks, and the carrier cutoff. Selecting only easily followed orders produces a clean-looking but biased picture. When an order is unfinished at observation end, keep it visible as unfinished rather than silently deleting it. For multi-line orders, establish whether timing ends at the first line or the complete order. Include all three lines in the latter case, because the customer receives the order only after its final requirement is satisfied.
Turn the analysis into a bounded decision. Describe the proposed change, the mechanism expected to alter performance, the measure that would detect the change, and the conditions under which it would be withdrawn. A small layout change might reduce walking yet increase congestion; an extra release wave might lower one queue yet overload picking. Monitor handover performance, first-pass accuracy, work in process, and staff workload together. Treat the proposed numbers as planning assumptions until a comparable observation period supplies evidence.
08 · Boundary and robustness review
Boundary and robustness review
Before implementing the selected countermeasure, check the boundary one more time. If the analysis starts after order release, an upstream acceptance hold is outside its measured lead time even though the customer experiences it. If the analysis ends at the loading bay, a parcel waiting for the carrier is still incomplete within the stated dispatch outcome. Keep those events inside the customer-facing boundary, or state exactly why a narrower operational measure is also being used.
Assess robustness across normal variation. A proposed operating rule should specify what happens when an urgent order arrives, stock is unavailable, a staff member is absent, or the carrier changes collection time. Those conditions do not invalidate the main analysis; they define where its assumptions need adaptation. Rehearse an exception through the proposed route with the people responsible for each decision. Record which assumptions remain unverified and what evidence would be sufficient to proceed.
Finish with an explicit learning statement: what the evidence currently supports, what it does not establish, and which observation is needed next. A quantified hypothesis can be useful without becoming a guaranteed result. Retain the current-state observations so a later comparison can use the same event definitions and population. When the observed outcome differs from the prediction, revisit the mechanism and resource assumptions rather than adjusting the target after the fact.
Connections
Related methods and phase use
Placed under Analyze because of the outcome it supports. Use the method in other phases when its purpose and assumptions fit the work; the phase list is a guide to selection, not a compulsory sequence.
Sources
Professional foundations and further reading
The explanation and fictional teaching examples are written for LeanTrainingLab. Linked primary sources provide professional foundations; example values and local conventions are stated in the guide. The accepted toolset draws on Six Sigma+Lean Toolset, second edition (Lunau, editor; Springer, 2013). No book text or examples are reproduced here.