Differences between a Gantt chart & a network diagram

Written by stephen byron cooper Google
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Differences between a Gantt chart & a network diagram
The arrival date of supplies is imortant to planning a critical path. (Getty Thinkstock)

Project planners have many tools available to plan the length of a project, its steps, duration and resource requirements. Two of the methods available use graphical representation of the tasks in the project and organise those into charts. One of these is called “Critical Path Analysis,” which requires the creation of a “network diagram.” The other of the two graphical methods is called a “Gantt chart.”

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Purpose

Both Gantt charts and network diagrams recognise the fact that several tasks contributing to a project can be undertaken simultaneously. The network diagram specifically aims to map out which tasks are dependent on the completion of others, and then represent this dependency as a “network.” The Gantt chart also depicts the start and finish point of each task and offsets the start date of each task to account for any requirements that task has from feeder tasks.

Network diagram

Several paths reach out from a single starting point and will end the timeline back at one point. In between the start and finish, each path shows a chain of dependent tasks. The aim of this layout is to find the shortest length of time the project can be completed. This is achieved by either prioritizing or delaying specific paths to satisfy the preconditions that certain tasks require. Once the diagram is complete, the planner highlights the path that has the deepest impact on the timeframe of the project. This is the “critical path.” Delays in that path will delay the entire project.

Gantt chart

The Gantt chart is a horizontal schedule that lists each task on a line by itself. A time series runs along the bottom of the chart. The scale of the time series (days/weeks/month) depends on the size and likely duration of the entire project. The planner charts the start and end date of each task and then shades in the line between those two dates. The start date of each task depends on task dependencies and availability of resources. For example, if the planner knows it will take two weeks for materials to arrive, there would not be any point scheduling the start of a construction task until the beginning of week three.

Differences

The main difference between the Gantt chart and the network diagram is their appearance. The network diagram looks like a plan of a network, but the Gantt chart looks more like a bar chart. The Gantt chart recognises that tasks are dependent on the completion of other tasks for their start date, but it does not specifically depict that relationship the way the network diagram does. The critical path is a key aim of both forms of plan, but the network diagram explicitly displays that path, whereas the Gantt chart doesn’t.

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