As an user experience designer and former graphic designer, I know that the way that information is displayed is most of the times as important as the content of the information itself. That being said, there are some scientific, quantifiable factors behind Information Design, and there are also some non-quantifiable variables, that we may agree on calling Art.
The Five Hats Rack principle is on the scientific side of Information Design, since is intended to organize and displaying information on a limited and quantifiable way: any type of information, regardless of the specific application, can be organized by Category, Time, Location, Alphabet and Continuum.
Category reflects to grouping by similarity or relatedness. For instance, if we're organizing animals we might want to divide them by species; on an online retail website, an organization by category (clothing, electronics, appliances, etc.) would probably be the most useful for customers. Now, let's say that we're soccer fans and want to design a chart with all the countries that have won the World Cup. The two obvious categories for this would be countries that have won the cup and those who have not; we might want to add a category with the runners-up, as well.
Time is simply the organization by chronological sequence: a TV guide schedule, a timeline of events, a recipe. In the case of our Soccer World Cup chart, we might want to display a timeline with all the tournaments and their host countries.
Location refer to organization by geographical or spatial reference. Any map is an example of this type (subway maps as well, for even when they do not utilize an exact map, there is a spatial reference between stations). If we wanted to include this type in our Soccer World Cup chart, we might include a world map with all the federations that participate on the FIFA tournament.
Alphabet means organization by alphabetical sequence. Dictionaries, directories and indexes are organized this way. This type of organization is used alone only when no other way of organizing is appropriate. In the example of the Soccer World Cup chart, we may want to list all the countries who have participated on the tournament, indicating how many times they have been present.
Finally, Continuum (sometimes called Hierarchy ) refers to organization by magnitude: low price to high price, most popular songs, etc. This is useful when there exist a common measure to compare different items of a group. We could include in our example chart a list with the countries who have won the cup more times, or a list with the all-time top scorers.
These strategies for organizing and displaying information are rarely used alone. Normally two or more are used, and sometimes all of them are necessary for explaining some complex information. You can see a chart with the example of the Soccer World Cup I used on my website , where I incorporated all five types of organization into one diagram.