Bubble versus Functional Diagrams – why is there a difference

July 17, 2009

I tend to treat bubble diagrams and functional diagrams as two different analysis tools.  They are often referred to synonymously but I think they have different roles in the design process.  Part of the confusion is simply an issue with how they may be drawn causing them to look slightly different.  The more important difference lies in how they are used.

Bubble diagrams are composed of shapes, typically round or oval, hence the name “bubble”.  They are intended to be drawn quickly as a tool for evaluating space usage and allocation.  Bubble diagrams can be used for ideation, adjacency analysis, traffic flow analysis, space allocation analysis, and other types of assessment.  They can also be used as a recording tool when making notes or on-site diagrams to identify specific areas or spaces on the property.  An important distinguishing element of the bubble diagram is that it has a lot of “white space”.  Bubbles can touch, overlap, or be separated from one another.  But just the fact that the bubbles are circle creates a large amount of white space on the diagram.  That is a good thing since the intention is to use the bubble diagram as an assessment tool.  There is frequently a lot of visual clarity in a bubble diagram because of its limited number of elements and the often distinct segregation of shapes.

Bubble shapes can have different relationships

Bubble shapes can have different relationships

Functional diagrams are also composed of shapes but tend to be more irregular.  Where bubble diagrams are used for analysis and assessment, functional diagrams are used more for representation and depiction.  Functional diagrams do not have large amounts of white space like bubble diagrams.  Their shapes are closer together representing the proximity of the spaces.

Functional diagrams have irregular shapes with close proximity

Functional diagrams have irregular shapes with close proximity

A functional diagram can be drawn to show the placement of existing elements on a site that is being evaluated.  They can also be used to depict the placement of design elements that are being considered in a particular arrangement.  A series of bubble diagrams may be evaluated to develop ideas and analyze potential arrangements.  When one of those diagrams is chosen as a potential solution, a functional diagram would show the proximate relationship of the design elements.  Since the functional diagram is free-form, it can be drawn quickly and used to validate the analysis and assessment of that particular design.

Typically, the way that I might use these two tools would be to first create a rough functional of the existing site elements.  This is done on blank paper or on a copy of the site survey.  When I am ready to start the ideation process, I use bubble diagrams to lay out potential combinations of design elements.  These alternatives are assessed in term of how they work together, traffic flow, allocation of space, and visual appeal.  Once one particular design pattern that is best is identified, I quickly convert it to a functional layout for further analysis and assessment.

Both bubble diagrams and functional diagrams are very useful analysis and assessment tools.  Bubble diagrams a usually quicker and easier to prepare and have the advantage of being an excellent tool at the ideation stage.  Once those ideas are solidified, the functional diagram gives the designer a much closer approximation of the actual design to use for further analysis and assessment.

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