"Dashboard elements accompanied by superfluous graphics make visual search more difficult (left). Dashboard elements without unnecessary icons make the numerical data more visually salient (right)."

UI example (from article) showcasing visually salient design

The UI of a complex application can have much information present on screen at once. As such, designers need to distinguish the most important information by having it be visually salient to the users, This can mean not only adding weight to a UI element, but also by removing non-essential elements from nearby. 

University of Michigan - Ann Arbor

Complex applications are extremely diverse. However, they do have general issues they can face, even across different applications. These 8 guidelines can help address those general issues and improve user efficiency.   
 
1. Promote learning by doing.
2. Help users adopt more efficient methods to do their tasks.
3. Provide flexible and fluid pathways through workflows.
4. Help users track actions and thought processes.
5. Coordinate transition among multiple tools and workspaces.
6. Reduce clutter without reducing capability.
7. Ease transition between primary and secondary information.
8. Make important information visually salient.

8 Design Guidelines for Complex Applications

https://www.nngroup.com/articles/complex-application-design/?utm_source=Alertbox&utm_campaign=f1070d165d-ComplexApps_AR_RemoteFieldStudies_20201109&utm_medium=email&utm_term=0_7f29a2b335-f1070d165d-40626629

Users prefer to start working with a system immediately, no matter how complex the system might be. They usually want to start completing tasks without having to worry about reading documentation or following tutorials. This means that many users learn by trial and error. Designers should work to support this type of learning by allowing them to experiment safely. Offering previews of the result of an action in the system can offer this type of support. 

 1 - Promote Learning By Doing

 Most users do not become expert users on their own. After some time, users will become stagnant with their efficiency with a system. They will keep using methods that might be inefficient but still familiar/satisfying to use. This can reduce productivity, so designers should try and implement ways to inform the user of more efficient methods. These designs should inform users in a non-obtrusive manner (not long tutorials). 

2 - Help Users Adopt More Efficient Methods

Users often have unstructured goals in a complex software. As such, they don't often follow a linear task flow, as they need to analyze and adapt their goals over time. Designers should support this by avoiding designs that force users to complete a task from start to finish with no way to exit.  

"For example, provide methods that allow for skipping ahead, looping back to an earlier step, and moving fluidly from any step to any other."

3 - Provide Flexible and Fluid Pathways

Data is complex apps can be overwhelming to users. Especially if the data takes a long time to compile and might be faced with interruptions. Designers should then allow for users to keep a record of their actions/thought process during their task. An example might be to have an open-text box that users can write comments in while processing data. 

4 - Help Users Track Actions and Thought Processes

Users of complex applications often have to switch between different types of software to support their work. This can include accessing an external database or other forms of documentation. As such, designers should design for this by making features that support exporting and importing data from other platforms. For example, being able to import or export data from Microsoft Excel. 

5 - Coordinate Transition Among Multiple Tools and Workspaces

Complex applications can be very cluttered, as they intend to support a wide range of uses and features. Complex applications must also support both new and expert users . With this in mind, designers should try to reduce clutter without reducing capability as much as possible. 


6 - Reduce Clutter Without Reducing Capability

Large-scale information can be overwhelming to users if displayed all at once. As such, designers should create different layers to information (primary and secondary). It is important to showcase primary information first. Secondary information should be available without leaving the primary information screen. For example, hovering on a piece of information will reveal secondary information. 

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