Computer-based visualization systems provide visual representations of datasets intended to help people carry out some task better (T Muzner).

The questions ensues with this definition is

- What are visual representations?
- What are datasets?
- How does the system help people?
- What sort of tasks people do? (Problem definition)

I'm especially interested and task oriented design and want to learn more about how do we best determine the problem and validate it.

The model of data visualisation design process that I'm currently studying is one by Tamura Muzer.

According to the model proposed there are 4 steps to design process and validations associated with the steps. The model takes a top down approach where the decisions made at the top level affects the lower levels.

The 4 steps are
1. Characterize the tasks and data in the vocabulary of the problem domain.
2. abstract into operations and data types
3. design visual encoding and interaction techniques
4. create algorithms to execute these techniques

What evaluation methodology is appropriate to validate each of these different kinds of design choices is of importance for the visualisation design.

4 categories of validity are proposed (they as in users and you as a designer)-
1. wrong problem: they don't do that 
2. wrong abstraction: you are showing them the wrong thing
3. wrong encoding/iteration: the way you show it doesn't work
4. wrong algorithm: your code is too slow.