Data Flow Diagrams

See also: ArcGIS DFD Examples (for Desktop or Pro)

Examples of student DFD's

Non-GIS DFD Examples

 

Data Flow Diagrams (DFD's) can be used to graphically illustrate the flow of data (a series of steps or analytical processes) through a system or model. More generically, Flow Diagrams (or Process Flow Diagrams) can be used to depict the movement and process steps of data, information, people, money, electricity, etc. The basic concept is to use a drawing as a means of illustrating what goes in (to a system or model), what processes occur (within the system or model) and what comes out (the results). Data Flow Diagrams are often created by drawing boxes, circles or other shapes to represent data and/or steps or decisions. The shapes are connected by lines or arrows which indicate sequence and relationships. Also known as a Flow Chart.

 

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A DFD for a GIS model or process should include (at a minimum) all of the necessary information for you (or someone else) to recreate the entire sequence of steps used to arrive at a conclusion or data output. This would include:

  • Names of input data file(s)
  • Names of process steps (clip, buffer, overlay, select by attribute)
  • Parameters used (.5 mile buffer, Name = New York, etc)
  • Names given to data layers being generated (big_streets, school_buff)
  • Arrows connecting the data (boxes) with the process steps (ovals) indicating the direction (flow) of data and the order of processing steps

 

 

In addition, a DFD can include (either as annotation or footnotes):

  • A name or title for the entire process
  • Source(s) of input data (where you got it)
  • Location where data (inputs and outputs) are stored
  • Optionally an abstract or summary of the goal/purpose

 

 

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Different flow diagrams (charts) use different symbology (shapes of boxes, colors of lines, etc) to communicate, but the principals are fairly similar.

 

The following symbols are commonly used in many Data Flow Diagrams (but Not in ArcGIS):

  • Input Data (Information sources) are represented by square boxes
  • Processes are represented by labeled ovals (bubbles)
  • Output Data are represented by rectangular boxes
  • Data flows (connections) are represented by a labeled arrow
  • Process parameters can be annotated on the flow diagram or footnoted

 

HOWEVER... The ModelBuilder in ArcGIS swaps the rectangles and ovals... Thus for ENVS. You can also use the drawing tools in Microsoft Word or PowerPoint to create DFD's, and this may be the simplest option, especially if you are planning on embedding the DFD into a written report or presentation. If you are using Word or PowerPoint note that you can create custom shapes (ovals, rectangles) using the Insert menu and you can connect these shapes via straight or curved connectors. Text and color can be added as desired. Note that for simplicity, the example below lacks annotation of parameters, data paths, etc.

 

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