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Data Visualization Foundations

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Histograms

2:21 with Anwar Montasir

The most obvious visual difference between histograms and bar charts is in the way the rectangular bars are presented: in histograms, the bars touch, whereas bar charts have space separating each bar. But how do we know when to use each one?

Vocabulary

What is a histogram?

  • Shows the distribution of numerical data
  • X-axis consists of bins containing ranges of numbers
  • X-axis uses continuous numbers
  • Vertical bars touch each other

Further reading

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    I'm looking at a blog post on the differences between histograms and 0:00
    bar charts. 0:04
    The blog post contains illustrations reminding us how to tell them apart. 0:06
    The most obvious visual difference is in the way the rectangular bars 0:11
    are presented. 0:15
    In histograms the bars touch whereas bar charts have space separating each bar. 0:16
    But how do we know when to use each one? 0:22
    The answer lies on the x-axis. 0:26
    Bar charts visualize discrete categories of data. 0:29
    Let's say I'm coaching a basketball team. 0:33
    I can use a bar chart to illustrate each player's free throw percentage. 0:36
    The order in which the data is displayed can be reordered. 0:41
    I could put the names alphabetically, or 0:44
    from highest to lowest percentage, depending on the story I want to tell. 0:46
    Histograms, on the other hand, 0:52
    show continuous data on the x-axis using ranges of numbers. 0:54
    We could present my players' free throw percentage as a histogram, 0:58
    if we visualize how many players make between 50 to 60% of their free throws, 1:04
    or 60 to 70, 70 to 80, 80 to 90, or 90 to 100%. 1:10
    Each range of numbers on the x-axis of a histogram is called a bin. 1:16
    You'll notice that the bin labeled 70 to 80 is empty since none of my players 1:22
    have a free throw percentage within that range. 1:27
    But I can't remove that bin from the x-axis, otherwise my chart gets confusing. 1:30
    I also can't reorder the bins. 1:36
    The height of the rectangles in a histogram represent the frequency of data 1:39
    points in each bin. 1:43
    Since 5 players hit between 80 and 90% of their free throws, 1:45
    that's the tallest rectangle. 1:49
    So let's review. 1:52
    A histogram shows the distribution of numerical data. 1:54
    The x-axis on a histogram consists of bins, containing ranges of numbers. 1:58
    The x-axis uses continuous numbers, 2:04
    meaning you can't rearrange them or skip a bin. 2:07
    And the vertical bars on a histogram touch each other. 2:11
    Hungry to learn more? 2:16
    In our next video, we'll take a look at the pie chart. 2:17

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