Idiot\'s Guides Basic Math and Pre-Algebra

262 Part 4: The State of the World

Bar Graph ......................................................................................................................................

Bar graphs are just what they sound like: graphs that use bars to compare different quantities.

The bars are usually vertical, but it is possible to make a horizontal bar graph, too. Each bar

represents a different quantity, and the height (or horizontal length) of the bar corresponds to the

size of the number.

When to Use It

Bar graphs are usually used to compare the sizes of different categories of information. The labels

on the horizontal axis are usually the names of the categories, and the heights of the bars show

the sizes of each category. The bars may be in size order (in which case the graph is sometimes

called a Pareto chart) or in some order that makes sense for the categories.

Bar graphs can also be used to show the change in some value over time, although a line graph

is probably a better choice. In that case, the labels on the horizontal axis may be dates, months,

years, or other time intervals.

How to Draw It

If you wanted to show the relative sizes

of the four classes in County High

School, you might make a bar graph,

with a bar to represent each class. If the

freshman class has 583 students, the

sophomore class 529, the junior class 492,

and the senior class 451, you’d want to

draw a horizontal axis with a space of

equal size for each of the bars. Usually,

you leave a little space between the bars.

Then you’ll need a vertical axis with

a scale that lets you show the different

class sizes. The largest class is 583, so

your vertical axis needs to go at least

that high, and it needs to be divided into

small enough units that you can find 583,

529, 492 and 451. If you try to do a scale

from 0 to 600 by tens, you may run into

a problem.

y

x

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