These are:
- Principle of pictorial realism
- Principle of the moving part
The principle of pictorial realism means that the objects that form the different parts of your computer program should look like how a human would visually interpret them. For example, if we were writing a car simulation application, and we were representing the speed of the virtual car in our application, we would use a speedometer – as this is what a human would associate with telling the speed of a car in the real world. Also, we would have the pointer on the speedometer move round and point further to the right the higher the speed of our virtual car. This makes it easy for a user to understand and makes it realistic. Although we could have the speedometer go from right to left rather than the standard left to right this would cause confusion and a greater learning period required for the user, and, although they would eventually become used to it, it creates an additional workload on the users mind and cognition that is not required.
There we have looked at a simple, one element situation. If there are multiple elements, as there will be in most apps, it is important that when all the elements are put together on the screen that they represent the environment as it would appear in the real world. For example, using our virtual car app, you wouldn’t put the accelerator on the passenger side, as this is not how it would be represented in real life and again causes unnecessary confusion for the user.
The basic idea of this principle is that when representing system objects and values visually, make them look like how they would appear in the real world and / or how the user would expect that they would appear. If there are certain well accepted standards for the type of application that you are developing, be sure to include these. Users like familiarity!
The principle of the moving elements ties in with the principle mentioned above. Users will have a cognitive model on how they expect something to move. In our example above, the user will expect the speedometer pointer to move further right the higher the speed that the virtual car is travelling.
It is important to work out and analyse, prior to developing your application, what you target user set expects and how they would visualise it in their minds. Then you should match the expected cognitive (mental) models of these users to how your application works and performs tasks. To not comply with this will only frustrate the users of your application – and if you are trying to get users to change over to a new application, then you want to do everything you can to make the transition as smooth as possible.