A bubble diagram in architecture is a freehand sketch in which each room or activity is drawn as a circle, roughly sized to its area, and linked to other circles by lines that show how strongly they need to be near each other. It tests the relationships in a brief before any wall, grid or dimension is fixed.
Students often meet it as one loose sketch at a pin-up. In practice it sits in the middle of a chain: an adjacency matrix feeds it, and a scaled block plan comes out of it. Skip the first and the bubbles are guesses; skip the last and they never become a building. Below, the whole chain is worked through on one example, a small branch library.
What Does a Bubble Diagram Show?
A bubble diagram shows three things at once: which spaces exist, roughly how big each one is compared with the others, and which pairs must touch, sit near each other, or stay apart. It says nothing about shape, structure, orientation to a street grid or exact area. That restraint is the point.
Each bubble is a function, not a room with walls. A thick line means a strong need for closeness, a thin line a weaker one, and a zigzag line can flag a pair that must stay apart for noise, security or smell.
Software that supports architectural programming uses the same visual grammar. The Vectorworks help documentation on creating a bubble diagram notes that a bubble diagram can be generated automatically when an adjacency matrix is imported, and that thick links indicate a strong relationship while weak ones are drawn with thin lines.
For where it fits beside parti, zoning, section and massing studies, see the overview of 21 types of architecture diagrams.
Where It Sits in the Design Process
The bubble diagram belongs to programming and early schematic design, after the brief is written and the site studied. A good site analysis should already be on the wall, because entrances, noise and daylight will pull bubbles in particular directions.
William Peña and Steven Parshall's Problem Seeking: An Architectural Programming Primer (5th edition, Wiley, 2012) sets out a five-step programming procedure that includes techniques for functional relationship analysis. The bubble diagram is the most direct way to draw that analysis.
The wider planning stage, including zoning and human scale, is covered in space planning architecture basics.
Step 1: Build the Space List
Everything starts with a list of spaces and their target areas. A course assignment from City Tech, CUNY frames it plainly: once you know the functions and the users of the building, you should be able to list every space it needs, organised by a system such as size or importance.
For our worked example, take a small branch library with eight spaces. The areas below are illustrative study figures for this exercise, not code or standard values:
- Entrance lobby (40 m²)
- Circulation and help desk (25 m²)
- Adult collection and browsing (180 m²)
- Children's area (90 m²)
- Quiet reading room (60 m²)
- Community meeting room (70 m²)
- Staff workroom (35 m²)
- Restrooms (25 m²)
Keep the list to functions that need their own location. A store cupboard inside the workroom does not deserve a bubble yet.
💡 Pro Tip
Group the list before you fill the matrix. Tag each space as public, semi-public or staff only. When you later draw bubbles, those three tags become three colours, and the zoning pattern of the building often appears on the first try instead of the fifth.
Step 2: Fill the Adjacency Matrix
An adjacency matrix is a grid that rates the relationship between every pair of spaces. The common form is a triangle: spaces are listed down one side, and each diamond-shaped cell where two rows meet holds one rating. The CUNY assignment describes the matrix as an in-depth look into how each space relates to the others in the building.
The rating scale has an industrial origin. Richard Muther's Systematic Layout Planning uses a relationship chart with six closeness codes, which the SLP overview by Richard Muther & Associates lists as A (absolutely necessary), E (especially important), I (important), O (ordinary closeness OK), U (unnecessary) and X (not desirable). Studios often simplify this, but keep the X code: separation needs are as real as adjacency needs.
Healthcare planners publish the same tool. In the U.S. Department of Veterans Affairs space planning criteria (PG-18-9), Chapter 106 on the Small House model rates relationships as high, moderate or minimal in a functional relationship matrix, then follows it with functional diagrams.
📌 Did You Know?
The number of pairs grows fast. Muther's relationship chart counts them as N × (N - 1) ÷ 2, so 8 spaces give 28 pairs, 12 spaces give 66 and 20 spaces give 190. That is why large briefs are rated by department first and by room second.
Adjacency Matrix for the Library Example
Here are the key pairs from the library matrix, using a simplified four-level scale. Pairs rated "unimportant" are left out to keep the table readable:
| Pair | Rating | Reason |
|---|---|---|
| Lobby and help desk | A (essential) | Staff must see everyone who enters |
| Help desk and staff workroom | A (essential) | Returns and processing move between them all day |
| Help desk and children's area | E (important) | Supervision without a dedicated staff member |
| Lobby and meeting room | E (important) | Evening use while the library is closed |
| Adult collection and reading room | I (useful) | Readers carry books between them |
| Restrooms and lobby | I (useful) | Meeting room users need access after hours |
| Children's area and reading room | X (separate) | Noise conflict |
Write a one-line reason for every A and X rating, so it can be checked against how the client actually operates instead of being argued at every review.
Step 3: Draw the Bubble Diagram
Now the matrix becomes a drawing, on trace or a loose digital canvas, in this order.
Size the Bubbles to the Program
Draw bubbles in proportion to their target areas: the 180 m² adult collection should look about seven times larger than the 25 m² help desk. Proportional sizing matters because a tiny bubble fits anywhere, while a large one has to find room.
Place the A Pairs First
Start with the strongest relationships and let the rest settle around them. In the library, the lobby, help desk and staff workroom form a tight chain of A ratings, so they become the anchor cluster. The children's area attaches to the help desk with a thick line, and the meeting room hangs off the lobby on the opposite side.
Push the X Pairs Apart
Next, check separations. The children's area and the quiet reading room cannot share a boundary, so they go to opposite ends with the adult collection as a buffer. This move often sets the long axis of the plan.
Mark Entrances and Outside Forces
Add arrows for the main, staff and after-hours entrances, and note the noisy street edge, the quiet garden side and the best daylight from your site analysis. The meeting room drifts toward the street so it can open independently, and the reading room moves toward the garden.
⚠️ Common Mistake to Avoid
Drawing the bubble diagram as a disguised floor plan, with squared-off bubbles that already butt together like rooms, defeats its purpose. If your bubbles already have corners, you have skipped a step. Keep them round until the relationships are settled, then switch deliberately to blocks.
Draw at least three versions. The Muther SLP overview states that the method requires two or more alternatives to be developed and evaluated before a plan is approved, and the same discipline helps in a studio. Compare them against the matrix by counting how many A pairs touch and whether every X pair is truly separated.
Step 4: Convert Bubbles to a Block Plan
A block plan, sometimes called a blocking diagram or stacking plan in multi-storey work, replaces bubbles with rectangles drawn at scale. This is the moment the diagram meets geometry, and it is where most weak bubble diagrams break.
Set a Grid and a Scale
Choose a structural or planning grid suited to the building type and draw at a working scale such as 1:200. Each block takes its exact target area from the space list. The 180 m² adult collection might become a 12 × 15 m rectangle, or a 9 × 20 m strip, depending on what the site allows.
Keep the Topology, Change the Shape
Translate each bubble into a block while preserving its neighbours. If two bubbles were linked by a thick line, their blocks must share a wall or an opening. If they were separated, keep a buffer block between them. Shapes will change a lot; neighbour relationships should not.
Add Circulation and Grossing
Bubbles leave out corridors, walls and plant, so the blocks add up to net area only; the building grows once those are added. Draw the main route as its own block. The guide to circulation diagrams in architecture shows how to separate public, staff and service routes, so the library's book return path stays out of the lobby.
💡 Pro Tip
Cut the blocks out of card or draw them as separate objects in your software, at the same scale as your site plan. Being able to slide blocks around the actual site boundary reveals fit problems in minutes, before you have spent hours refining a layout that cannot fit the plot.
Check the Block Plan Against the Matrix
Audit the block plan against the matrix pair by pair. In the library, the children's area and the reading room often drift together because both want garden light; the X rating says the plan changes, not the rule.
Only then does the block plan become a floor plan with walls, doors and furniture.
Bubble Diagram vs Adjacency Matrix vs Block Plan
The three drawings carry the same information in different forms:
| Aspect | Adjacency Matrix | Bubble Diagram | Block Plan |
|---|---|---|---|
| Format | Triangular grid of ratings | Circles linked by weighted lines | Rectangles at scale on a grid |
| Answers | Which pairs need closeness? | How can the pattern be arranged? | Does it fit the site and area? |
| Scale | None | Relative sizes only | Exact areas |
| Site input | None | Entrances, views, noise | Boundary, grid, setbacks |
| Best tool | Spreadsheet | Trace paper or tablet | CAD or BIM |
How to Present Bubble Diagrams on a Board
On a final board, the bubble diagram explains why the plan looks the way it does. Show the matrix, two rejected options and the chosen one left to right, with the block plan as the last frame.
Use the same three zone colours across matrix, bubbles and blocks, match line weights to the rating scale, and add a small legend. The architecture diagram collection in the store has ready-made vector bubbles, arrows and zone graphics you can restyle to your project colours.
Place it next to your concept diagram: one states the big idea, the other proves the idea can carry the brief.
What This Means for Your Next Project
Your Next Step: Before your next studio review, turn your brief into a space list and rate every pair in a triangular matrix, writing one reason for each "essential" and each "keep apart" rating. Then draw three bubble options from that matrix and pick one only after you have counted how many essential pairs it satisfies.
To start your own diagram, download our Free Circulation/Program Diagram Template.
Frequently Asked Questions
What Is the Difference Between a Bubble Diagram and a Zoning Diagram?
A bubble diagram shows individual spaces and the relationships between them. A zoning diagram groups those spaces into larger areas, such as public, private and service zones, and places those zones on the site. Many designers draw the bubble diagram first and then outline the zones around clusters of bubbles.
Do Bubbles Have to Be Drawn to Scale?
Not to an exact scale, but bubbles should be roughly proportional to their target areas. If every bubble is the same size, the diagram hides the hardest planning problem, which is where the largest spaces can fit. Exact areas come later in the block plan.
What Software Can I Use to Make a Bubble Diagram?
Pen and trace paper are fastest for early options; a tablet drawing app or Illustrator suits cleaner versions. Some CAD and BIM programs, such as Vectorworks, can generate bubble diagrams from an imported adjacency matrix.
How Many Spaces Should a Bubble Diagram Include?
Enough to show every function that needs its own location, usually somewhere between six and fifteen for a student project. Larger buildings are diagrammed in layers: departments first, then a separate bubble diagram inside each department.
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