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Introduction to Data Visualization

A beginner's guide to data visualization tools and techniques.

What are Data Types?

The data type is a classification for data that determines how data can be used by programming languages and data analysis software. Knowledge of data types is fundamental to visualizing data as the type of data will affect the possible visualizations which may be generated from that data.

Quantitative Data

Quantitative Data: 

Quantitative data is composed of numeric value.


  • Height
  • Weight
  • Age

There are two categories for quantitative data: 

  1. Discrete data is data that can only take certain values, typically in the form of whole numbers. Whole numbers are often referred to as integers by programmers.
  2. Continuous data is data that can take on any numeric value. This includes fractional values, such as values containing a decimal point. Data scientists often refer to these values as floating point numbers or just floats. 

Examples of Discrete Data:

  • The number of people in a room. (has to be a whole number, you can't have a fraction of a person).
  • The number of planets in the solar system. 

Examples of Continuous Data: 

  • surface area of a balloon (can be anything between surface area when totally deflated and when expanded to maximum size).
  • Body temperature (commonly measured using decimals).  

Qualitative Data

Qualitative Data: 

‚ÄčQualitative data categorizes or describes an object, but does not measure it. Qualitative data are typically recorded as text. Data scientists often refer to textual data as string data.  

There are three categories of qualitative data: 

  1. Categorical (nominal) data fall into groups or categories. 
  2. Ordered data: Categorical data that has an order of the categories. The distance between categories may not be equal.
  3. Binary data is qualitative data which only has two possible values. 

Examples of Qualitative Data: 

  • Categorical: religious affiliation (Buddhist, Christian, Atheist)
  • Ordered: education level (high school, undergraduate, graduate)
  • Binary: success or failure

Date-Time Data

Date and time data is typically represented as sets of numbers separated by dashes or colons. There is even a format recommended by the International Standards Organization for recording date and time data. 


ISO 8601 uses the following format for indicating dates: 


Where YYYY represents a four-digit year, MM is a two digit month between 01 representing January and 12 representing December, and DD for the day of the month with 01 as the first day of the month and 31 being the last possible day of the month.

As an example, the date February 9, 1995 would translate to 1995-02-09. 


ISO 8601 uses the following format for indicating time: 


Where HH represents the hour of the day on a 01-24 military time scale, MM represents the minute of the hour between 00 and 59, and SS represents the second of the minute, also between 00 and 59.

This is probably familiar, as it is commonly used with stop watches to record time.