A chart is a graphical representation of data, in which “the data is represented by symbols, such as bars in a bar chart, lines in a line chart, or slices in a pie chart”. A chart can represent tabular numeric data, functions or some kinds of qualitative structure and provides different into.
The term “chart”
as a graphical representation of data has multiple meaning.
Features of a chart.
A chart can take
a large variety of forms, however there are common features that provide the
chart with its ability to extract meaning from data.
Typically the
data in a chart is represented graphically, since humans are generally able to
infer meaning from pictures quicker than from text. Text is generally used only
to annotate the data.
One of the most
important uses of text in a graph is the title.
A graph’s title usually appears above the main graphic and provides a succinct
description of what the data in the graph refers to. Dimensions in the data are
often displayed on axes. If a horizontal and a vertical axis are used, they are
usually referred to as the x-axis and y-axis respectively. Each axis will have a scale, denoted by periodic graduations
and usually accompanied by numerical or categorical indications. Each axis will
typically also have a label displayed outside of beside it, briefly describing
the dimension represented. If the scale is numerical, the label will often be
suffixed with the unit of that scale in parentheses.
EXAMPLE:
“Distance traveled (m)” is a typical x-axis label and would mean that the distance traveled,
in units of meters, is related to the horizontal position of the data within
the chart.
Within the graph
a grid of lines may appear to aid in
the visual alignment of data. The grid can be enhanced by visually emphasizing
the lines at regular or significant graduations. The emphasized lines are then
called major grid lines and the remainders are minor grid lines.
The data of a
chart can appear in all manner of formats, and may include individual textual labels describing the datum associated
with the indicated position in the chart. The data may appear as dots or
shapes, connected or unconnected, and in any combination of colors and
patterns. Inferences or points of interest can be overlaid directly on the
graph to further aid A pie chart (or a circle chart) is a circular statistical graphic, which is divided
into slices to illustrate numerical proportion. In a pie chart, the arc length
of each slice (and consequently its central angle and area), is proportional to
the quantity it represents. While it is named for its resemblance to a pie
which has been sliced, there are variations on the way it can be presented. The
earliest known pie chart is generally credited to William Playfair’s
Statistical Breviary of 1801.
Pie charts are
very widely used in the business world and the mass media. However, they have
been criticized, and many experts recommend avoiding them, pointing out that
research has shown it is difficult to compare different sections of a given pie
chart, or to compare data across different pie charts. Pie charts can be
replaced in most cases by other plots such as the bar chart, box plot or dot plots.
EXAMPLE:
Pie chart of populations of English native speakers.
Actionnariat de Liberation (janvier 2007).
EXAMPLE:
Some people were asked what they had for breakfast.
The data is recorded below:
(a) Add up the number of people.
Total
frequency =
18 + 8 + 4 + 15 = 45
(b) Whole angle in a pie chart = 360⁰
This must be split between 45 people.
Angle for each person = 360⁰ ÷ 45 = 8⁰
Angle for ‘toast’ = 8 × 8⁰ = 64⁰
Angle for ‘egg’ = 4 × 8⁰ = 32⁰
Angle for ‘nothing’ = 15 × 8⁰ = 120⁰
Reading from pie charts.
EXAMPLE:
Marilyn has £120 to spend each week. The pie
chart shows what she spends her money on. How much does she spend on rent?
2/5 of £120 = (120 ÷ 5) × 2
= 24 × 2 = £48
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