The bulk of all data visualization takes the form of a simple chart, diagram or graph. In use across all varieties of business enterprise, a chart is simply is a graphical representation of data, in which “the data is represented by symbols, such as bars in a bar chart, lines in a line chart, or slices in a pie chart”. Charts ease understanding of data and demonstrate various interrelationships that occur between data sets. Charts are typically read and understood more quickly than simple raw, numerical data since the human brain is generally able to infer meaning from pictures much quicker than from text or numbers alone.
The nomenclature used for a chart is typically interchangeable with the terms ‘diagram’ or ‘graph.’ Regardless, they all refer to a diagrammatical illustration of a set of data. They are most often created by hand (sketch) or by computer using a charting application like Microsoft Excel®.
Rather than attempting to draw distinctions between a chart, diagram or graph, it is more valuable to understand which types of charts are more useful for presenting a given data set over another. For example, data that is represented in percentages (fractional share, preference or departmental) is often displayed in a pie chart. Comparing the sum totals of particular sets of data (number of instances), on the other hand, may be more easily understood when presented in a vertical bar chart. Or, data that represents numbers that change over a period of time (revenue, expenses or staffing) might be best shown as a line chart.
Common Types of General Charts, Diagrams & Graphs:
Bar Chart: A chart with rectangular bars having lengths proportional to the values that they represent. The bars can be plotted vertically or horizontally. A vertical bar chart is sometimes called a column bar chart.
Line Chart: A type of chart which displays information as a series of data points called ‘markers’ which are connected by straight line segments. Information is most typically presented as a time series with the x-axis moving chronologically from left to right. Earned value calculations on projects take the visual form of a line chart.
Pie Chart: A circular statistical graphic, which is divided into sectors to illustrate numerical proportion, or percentage of the whole. In project management, this is used frequently to display the breakdown of different resource or cost types.
Radar Chart: A graphical method of displaying data for two or more variables in the form of a two-dimensional chart of three or more quantitative variables represented on axes starting from the same point. (also known as a Spider, Web or Star Chart). Radar charts are popular for showing pre- and post-event changes, such as process improvement measurements.
Bubble Chart: A type of chart that displays three dimensions of data. Bubble charts are frequently used to facilitate the understanding of social, economic, medical, and other scientific relationships. In project management discipline, it is very commonly used as a way to map out project portfolio investment balance and is typically presented to show strategic alignment (x-axis), impact (y-axis) and size of effort (data point size).
Waterfall Chart: A type of chart used to depict the cumulative effect of sequentially introduced positive or negative values. Demonstrates how an initial value is affected by a series of intermediate positive or negative value-based events. For project management applications, waterfall charts are used to show costs versus expected payback.
Shared Attributes of General Charts, Diagrams & Graphs:
Charts share a number of similar features that make it easier to understand what the data represents and serve as a frame of reference for viewer:
- Bar, line and other similar charts often display data on a field of axes. Horizontal (x) and vertical (y) axis frame the field in which the data is analyzed. On some occasions where the data is presented in 3D format, the depth (z) axis is added.
- Each axis must have a Scale provides the ratio of the size of a model or other representation to the actual size of the object represented. Scale is frequently sub-divided by periodic graduation marks to aid the viewer in spatial reference.
- Each axis will typically also have a label displayed outside or beside it, briefly describing the dimension represented.
- Within the graph, a grid of lines may appear to aid in the visual alignment of data. Using the appropriate scale, major and minor grid lines can be set, with major grid lines typically being enhanced or emphasized to define the intervals.
- The data of a chart can be represented in any number of formats. For example, data may appear as dots, lines, symbols or shapes. The individual data points can be connected or unconnected, or they can take on any combination of colors and patterns.
Legend or Key
- When the data appearing in a chart contains multiple variables, the chart may include a legend (also known as a key). A legend contains a list of the variables appearing in the chart and an example of their appearance. This information allows the data from each variable to be identified in the chart.
Common Types of Project Management Charts, Diagrams & Graphs:
Gantt Chart: A type of bar chart, developed by Henry Gantt in the 1910s, that illustrate a project schedule. Summary task, task level and milestone elements of the work breakdown structure of the project comprise what is typically represented on the Gantt chart. Gantt charts can also show dependency (i.e., precedence network) relationships between activities and tasks. Gantt charts can also be used to show current schedule status using percent-complete shadings and a vertical marker line to represent the current date.
Project Network Diagram (PERT Charting): A graphical flow chart that depicts the sequence of a project’s detailed task-level elements, including all pertinent dependencies. The project network diagram is drawn from left to right to reflect project chronology. Modern day project network diagramming is a derivation of a more complex, but similar, past technique known as ‘PERT.’
PERT is the acronym for Program Evaluation and Review Technique, which is a method of analyzing all of the tasks involved in completing a given project, especially the time needed to complete each task, in order to identify the minimum time needed to complete the total project, also known as the ‘critical path.’ Developed primarily to simplify the planning and scheduling of large, complex and interdependent projects, it was developed for the U.S. Navy Special Projects Office in 1957 to support the U.S. Navy’s Polaris nuclear submarine project.
Many more charts, graphs and diagrams, including a number of additional project management specific tools, along with over twenty-five other visual project management communication concepts, are explored in greater detail within “Visual Project Management,” a recently released publication by Paul R. Williams, and now available to interested readers!