William Playfair invented the line chart, bar chart, and pie chart in the late 18th century, laying the foundations of modern data visualization. Charles Minard and Florence Nightingale also made important contributions, with Minard combining data with maps and Nightingale persuasively presenting data to Parliament. Effective graphs convey complex data at a glance, reveal relationships between variables, and help reason about quantitative information.

1. HOW TO GRAPHICALLY
Represent Data
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2. A BRIEF HISTORY OF VISUALIZING QUANTITATIVE DATA
➤ Visually representing numbers is a new invention.
➤ It was not until 1750-1800 that statistical graphics were
invented.
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3. THE WORK OF THREE PEOPLE FOUNDATIONAL TO MODERN GRAPHICS:
➤ William Playfair (1759-1823) a Scottish engineer and
political scientist invented three types of graphics: the line
chart, bar chart, and pie chart.
➤ Charles Joseph Minard (1781-1870) a French civil engineer
created cartographic representations of data — combining
data with maps to display the flow of people and goods.
➤ Florence Nightengale (1820-1910) a nurse, statistician, and
medical reformer innovatively visualized data in her
persuasive reports to the British Parliament in easy-to-
understand informational graphics.

4. WILLIAM PLAYFAIR’S GRAPHIC REPRESENTATIONS
And I did not use Excel.
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5. MINARD’S GRAPHIC OF NAPOLEON’S ARMY INVADING RUSSIA IN 1912:
➤ Six variables are plotted and the take away here is to realize
that graphics can convey a high level of complexity if
handled right.
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6. NIGHTENGALE’S REPORTS TO PARLIAMENT:
➤ Include graphics she created to her support arguments about
the need for medical reform. She graphically represented data
using standard bar charts, but she also visualized data in an
innovative way.

7. NIGHTENGALE’S COXCOMB OR POLAR CHART:
➤ displayed causes of deaths of soldiers during the Crimean
war. It conveyed, at-a-glance, how more soldiers died from
infection than from wounds.

8. ANSCOMBE’S QUARTET
➤ The statistician F.J. Anscome demonstrated the importance of graphically
representing data before analyzing it.
➤ The quartet consists of four sets of data that have identical simple statistical
properties. Yet, when graphed, they are very different.
➤ Anscombe’s quartet shows how graphics do not just report data, they reveal
data, and they are instruments for reasoning about quantitative information.
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9. DATA MAP: SCATTER PLOT
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10. RELATIONAL GRAPHICS
➤ did not appear in scientific writings until the late 1700’s.
This drawing by Johann Heinrich Lambert shows the periodic
variation in soil temperature in relation to the depth under
the surface.
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11. PIE CHARTS REPRESENT PARTS TO WHOLE
➤ They are most often used to present percentages of parts to a
whole.
➤ Limit the chart to no more than seven sections.
➤ Use contrasting colors or shading.
➤ Label the segments.
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12. BAR GRAPHS: COMPARE TWO TYPES OF INFORMATION ON EACH AXIS
In a horizontal bar graph,
neither axis is a measure of
time.
In a vertical bar graph, the x
axis is ordinarily the measure of time.
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13. STACKED BAR GRAPH
➤ Can convey a great deal of information but it may not show
what the data means as clearly.
➤ In this graphic, Africa’s population increased by more than
100% while Non-OECD Asa increased by about 50%
While the chart is
beautiful to look at,
the meaning is not
clear.
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14. COLUMN GRAPH OR BAR CHART
➤ For a vertical bar graph, start the y axis at zero and use equally
spaced intervals. For the x axis, equally space the intervals.
➤ For a horizontal bar graph, start the x axis at zero and use equally
spaced intervals. For the x axis, equally space the intervals.
➤ Label all information on the x and y axis.
➤ Limit the number of divisions. Too many will make the data difficult
to read.
➤ Use color or shading to distinguish divisions.
➤ Avoid crowding.
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15. LINE GRAPH
➤ The purpose of a line graph is to show the degree and direction of
change relative to two variables. It is a relational graphic.
➤ Choose the scale of each axis to show an appropriate representation of
the data. If possible start each at zero.
➤ Equally space the intervals.
➤ Use color to differentiate
to differentiate the lines.
➤ Remember, the relationship
of the data has to make sense.
➤ Lines are not connected just
to make it easier to see them.
The slope of the line has to make sense.
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16. SCATTER PLOT
➤ Are similar to line graphs but have a very different purpose.
➤ They use horizontal and x axes to plot data points but the
purpose is to show a correlation between two variables.
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17. ALWAYS
➤ Label the graphic (figure 1, figure 2 etc.).
➤ Caption or title the figure.
➤ Refer to it in the narrative information you provide.
➤ Example:
Figure 1 compares the annual wages for three different jobs
in the field of professional writing.
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18. FOR ADDITIONAL READING: