Definition
A spaghetti diagram is a visual tool that traces the actual path of movement — of a person, a part, or a document — on a scaled floor plan of the workplace. An observer follows the subject through one or more complete work cycles, drawing a continuous line on the floor plan for every step taken. The resulting diagram typically looks like a plate of spaghetti — tangled, overlapping lines that reveal just how much wasted movement occurs in a process that may appear efficient from a desk.
Japanese Origin
The Japanese term dōsenzu (動線図) means “movement line diagram” — 動 (dō, movement), 線 (sen, line), 図 (zu, diagram). The concept is used broadly in Japanese facilities design, including architecture and retail layout, not just manufacturing.
History at Toyota
Spaghetti diagrams are a standard observation tool used at Toyota during kaizen activities, particularly when redesigning layouts or establishing standardized work. The tool is valued because it reveals a category of waste — excessive walking and movement — that is difficult to see through normal observation. An operator walking 200 meters per cycle looks busy. Only when the path is traced on paper does the waste become visible and measurable.
Toyota engineers use spaghetti diagrams as part of layout improvement activities, where the goal is to minimize operator walking distance by rearranging equipment, parts presentation, and workstation design. The before-and-after comparison of spaghetti diagrams is a powerful visual demonstration of improvement.
How It Actually Works
Creating a spaghetti diagram:
- Obtain or draw a scaled floor plan of the work area showing equipment, parts storage, tools, and walkways
- Go to the genba and observe the operator (or follow the part) through one complete work cycle
- Draw a continuous line on the floor plan tracing every movement — every step, every reach to a parts bin, every trip to a tool storage area
- Note the distance of each segment if possible
- Repeat for multiple cycles to confirm the pattern is representative
- Total the walking distance for one cycle
Reading the diagram:
- Dense, overlapping lines indicate areas of excessive movement
- Long straight lines reveal trips to distant locations (parts storage, tools, inspection stations)
- Back-and-forth lines between the same two points suggest layout problems
- The total distance per cycle quantifies the waste
Using the diagram for improvement:
- Redesign the workstation layout to bring parts and tools closer to the point of use
- Rearrange equipment to create a tighter flow path
- Eliminate trips by relocating storage or adding point-of-use inventory
- After implementing changes, draw a new spaghetti diagram to confirm improvement
Common Mistakes
Drawing the diagram from memory or from standardized work documents. The spaghetti diagram must trace actual movement, not planned movement. Operators often deviate from the documented path — reaching for parts in a different location, walking around obstacles, or taking detours. The diagram must be based on direct observation at the genba.
Tracing only one cycle. A single cycle may not be representative. Observe multiple cycles to capture variation — different model mixes, different operators, different times of the shift — before drawing conclusions.
Focusing only on operators. Spaghetti diagrams for material flow (following a part through the factory) and information flow (following a document or electronic signal) can reveal equally significant waste. The tool is not limited to operator movement.
Making improvements without redrawing. After changing the layout, draw a new spaghetti diagram to verify that the changes actually reduced movement. Sometimes a layout change that looks good on paper creates new movement problems in practice.