What is a graph on which values are represented as vertical or horizontal bars?

Graphic charts are used to present numerical data in an
easily understood fashion.  Charts can be drawn on a blackboard or easel pad, or
presented in the form of a computer or group presentation by slide show (PowerPoint
presentation).

When dealing with a small number of
categories, a column chart is convenient.  The categories (such as different years) are
listed along the x-axis (horizontal axis).  Columns (vertical bars) are placed at each
category and the columns' height on the y-axis (vertical axis) indicate the values.  An
example of a column chart would be a chart showing annual sales of a single company over
a five year time period.  Along the x-axis you would indicate each of the five years
(e.g. 2001, 2002, 2003, 2004 and 2005).  For each year you would draw a column whose
height would match the sales amount as read on the y-axis.  The column chart is the most
commonly used chart type for demonstration of simple
data.

A bar chart has opposite orientation.  This type of
chart can accommodate a greater number of categories that are listed on the y-axis.  And
because screens are usually wider than tall, you can list categories with longer names,
stacked horizontally along the y-axis.  An example of a typical bar chart would be a
comparison of populations of 20 major cities, listing the cities and their countries
along the y-axis on the left side of the chart.  The horizontal bars drawn for each city
would show the populations in thousands along the x-axis.

A
line chart is formed by plotting points for each quantity for each category, then
connecting the points with a single line. A good use for this type of chart would be
demonstrating the price of a given stock over time.  The months or years would appear
along the x-axis.  For each time period a dot would mark the price as shown on the
y-axis, and a line would be drawn connecting the points.  One would thus illustrate the
upward and downward price trends.

The reference explains
these simple charts as well as pie charts and scatter charts, and gives methods for
depicting more complex data with the chart forms.