In Data Visualisation there are 4 main data types which are Nominal, Ordinal, Interval and Ratio data types.
Nominal: Nominal data is data based on named categories and are unordered. This data can be counted but cannot have an average but can be used to calculate a percentage. When there is only 2 sets of data it is called Dichotomous data.
Ordinal: Ordinal data is data which is ordered where numbers are assigned to the categories to make the data easy to analyse. For example scores between 1-5 where 1 is bad and 5 is great or vice versa.
Interval: Interval data is the measuring of periods of time. The value of 0 doesn’t measure the absence of something and could mean the start of a new interval.
Ratio: Ratio data is the amount of something. 0 means an absence of something where there is nothing in that section or period of time.
These groups branch under the 2 data types which are Qualitative and Quantitative data.
Qualitative data is non numerical consisting of ordinal and nominal data.
Quantitative data is numerical consisting of interval and ratio data.
The different data types need to be considered before designing a visualisation depending on the approach of the visualisation as each data type has a different different outcome and visual approach to
Daniel Krivacic Data Visualisation 