Posted by Michael Gaigg
Before I dive into guidelines and tips of designing and implementing usable websites I feel it is important to define and outline what Usability is. Please allow me at this point to cite several sources that I find essential.
Usability is the
- Effectiveness (accuracy and completeness to achieve goals)
- Efficiency (resources expended in relation to the accuracy and completeness)
- Satisfaction (comfort and acceptability of the work system to its users)
with which specified users achieve specific goals in particular environments. [ISO9241]
Alan Dix formulates in his book 'Human-Computer Interaction' that above definition can be concluded into three basic principles:
- Learnability (the ease with which new users can begin effective interaction and achieve maximal performance)
- Flexibility (the multiplicity of ways the user and system exchange information)
- Robustness (the level of support provided to the user in determining successful achievement and assessment of goals)
Five Quality Components
Jakob Nielsen uses human characteristics to extend these principles by saying:
Usability has five quality components:
- Learnability: How easy is it for users to accomplish basic tasks the first time they encounter the design
- Efficiency: Once users have learned the design, how quickly can they perform tasks?
- Memorability: When users return to the design after a period of not using it, how easily can they reestablish proficiency?
- Errors: How many errors do users make, how severe are these errors, and how easily can they recover from the errors?
- Satisfaction: How pleasant is it to use the design?
with the addition of 'utility' (functionality): Does it do what the user needs?
Implications for Usability Design
Implications drawn out of above definitions are that pages shall strive (devote serious effort or energy) to provide:
- Consistency of presentation and controls across the site
- Logical and natural organization of information (clear structure, systematic, clear and meaningful labels)
- Contextual navigation (how much information is given for providing a context for the user; where is he/she in the site? Where can he/she go? How can he/she go back?)
- Efficient navigation (the amount of time and effort the user needs to exert in order to move around the site)
- Adequacy of feedback (are user interactions clear, are requests answered, do commands elicit the right response?)
- Searchability (how effectively the site content can be sought in search engines?)
Michael Gaigg is Lead UI Engineer in Esri's Professional Services Division.
He has been designing map applications for 15 years and is author and curator of UI Patterns for Maps.
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