Graphs
A graph is a diagram of values which shows the relationship between given information or data.
Some of the graphs studied in Grade 6 include bar graphs, double bar graphs, pie charts and pictographs.
Examples
Example of a Bar Graph
Example of a Double Bar Graph
Example of a Pie Chart
Example of a Pictogram
In Grade 7 we are going to study two types of line graphs, i.e., linear and nonlinear graphs.
Linear means in a straight line, so a linear graph is a graph that increases or decreases in a straight line.
Example of a Linear Graph
A nonlinear graph is a graph that increases or decreases in a curved or broken line.
Example of a Nonlinear Graph
The xaxis is horizontal and the yaxis is vertical.
The data on the xaxis (linear) in line graphs is usually constant.
The data on the yaxis in line graphs is variable (changing), i.e., either increasing or decreasing.
Parts of a Line Graph
We need to draw and label graphs properly so that the data can be read and interpreted accurately.
 The title or heading gives us an idea of what the graph is all about.
 The horizontal and vertical labels indicate the information being displayed.
 The scale, which is the range of values on the xaxis and yaxis, tells us the quantity of the information being displayed.
 The dots or points on the graph, shows the information that is being compared.
 The lines joining the dots, shows the pattern.
In the above graph the dots or points follow a regular pattern (2, 4, 6, …) which results in a straight line. A straight line indicates a linear graph. The line in the graph above has an upward slope, which indicates it is showing an increase in the data.
Drawing Graphs
We can draw graphs from information given.
Example
The table below shows the total monthly car sales at SA Motors over a year. We will use this information and follow the five steps below the table for drawing a line graph.
CAR SALES FOR ONE YEAR 

Month 
Cars Sold 
January 
13 
February 
25 
March 
30 
April 
22 
May 
47 
June 
29 
July 
36 
August 
40 
September 
52 
October 
44 
November 
56 
December 
65 
Step 1
Identify the range of values. In this graph there are two sets of values:
i) Months of the year: January to December
ii) Number of cars sold: smallest (13) to biggest (65)
Step 2
Select a scale, for example, in this graph, one block = 10 cars.
Step 3
Label the graph.
i) The xaxis (horizontal) in this graph is months of the year (constant – stays the same)
ii) The yaxis (vertical) in this graph number of cars sold (variable – changes)
Step 4
Plot the numbers or values using dots or points, then join the points or dots.
Step 5
Remember to give your graph a suitable title or heading, for example, for this graph, ‘Monthly Car Sales Over a 1 Year Period’.
The information is now clearly visual, so it becomes easier to study and interpret the graph by answering questions.
Example
a) How many cars were sold altogether in one year?
b) In which month was the most cars sold and how many cars were sold in this month?
c) Why do you think so many cars were sold in this month?
d) Why do you think so few cars were sold in January?
e) Is this a linear or nonlinear graph? Give a reason for your answer.
Answers
a) 460 cars were sold in one year.
b) December – 65 cars.
c) Answers will vary.
Possible answer could be: Many people get bonuses and save up the entire year.
d) Answers will vary.
Possible answer could be: Many people spend a lot during the festive season
and experience financial problems during the start of the new year.
e) Nonlinear graph, because the number of cars sold is not constant.
ACTIVITIES
Activity 1
Activity 2