Data Flow Diagrams
See also ArcGIS DFD examples)
See also a few examples of methods students have used to create DFD's)
See also, some non-GIS DFD examples)
(the basic format for a DFD)
Data Flow Diagrams (DFD) can be used to graphically illustrate the flow of data 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. through a system. The basic concept is a means of showing what goes in (to a system or model), what processes occur (within the system or model) and what comes out.
Here is a Definition of Flow Diagram from LingualLinks:
A flow diagram is a graphical means of presenting, describing, or analyzing a process. This is done by drawing small boxes which represent steps or decisions in a chain of steps or decisions. These boxes are connected to other boxes by lines and arrows which represent sequence and dependency relationships (i.e., X must be done before Y can be done).
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
Names of process steps (clip, buffer, overlay, select by attribute)
Parameters used (.5 mile buffer, Name = New York, etc)
Names given to data layers 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 should include (either as annotation or footnotes):
A name or title for the entire process
Optionally an abstract or summary of the goal
Source(s) of input data (where you got it, where its stored)
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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:
HOWEVER... The ModelBuilder in ArcGIS swaps the rectangles and ovals... Thus for Egeo350 note that the following symbols should be used (to match the ModelBuilder symbology):
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Notes on creating DFD's in Microsoft Word or Power Point.
Microsoft Word is probably the best program to use if you will be integrating flow diagrams into a report or other written document. Use the word processing capabilities to write you report, and then use the drawing toolbar to add a flow diagram. Power Point works almost identically to Word in terms of the Drawing Toolbar. Diagrams can be copied from one to the other. To use the Drawing Toolbar, click on Toolbars... under the View menu, and drawing tools will appear in icon form at the bottom of the page. There are tools to draw boxes and squares (icons on the Drawing Toolbar) as well as to add text to the same (text icon on the Drawing Toolbar). In addition, bent or curved lines can be added to connect the shapes (Drawing Toolbar | AutoShapes | Connectors). Note that connectors remain connected to their object even if the object is moved. To add text to your diagram click on the Text Box icon and then on the drawing. If you click in a box, you can add the text to that box. If you click outside of a box you will create a new text box. Box and circle outlines and fill color can be changed using the color icons on the Drawing Toolbar. Click on the object(s) to modify using the Drawing Toolbar Select Objects arrow and then choose the color. Choosing No Fill or No Line will produce a transparent outline or fill. Note that for simplicity, the example below lacks annotation of parameters, data paths, etc.
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