Graphing is a way to present data, concisely and visually. Using
graphs or charts can make it easier to see relationships in data. A
great deal of information is communicated using graphs and charts
in newspapers, television, books and other places. The ability to
read graphs and charts is necessary in making sense of the world
we live in.
The gathering and analysis of meaningful data includes asking and answering questions to help you make sense of your world. It is important that you apply your knowledge of data relationships to an organizational tool for sorting. Charts, diagrams and graphs are useful as tools to understand mathematical relationships and solve mathematical problems.
In Grade 3, you would have learnt how to collect and display data in pictographs and bar graphs. As you investigate a wider range of topics, you may discover that the data you collect is too large to display in a graph using a one-to-one correspondence (i.e. having each symbol or number on the bar graph represent one piece of data).
You need to learn the concept of using a many-to-one correspondence [or scale] when you are creating graphs to display large amounts of data. You need to make decisions about what symbol to use and what that symbol should represent. These decisions are based on the data being used.
For example, if you want to display a graph to show your marble collection and you have 36 blue, 24 red, and 42 clear, you may decide to draw a pictograph where each symbol represents 2 marbles or one where each symbol represents 6 marbles.
In cases where the numbers are all less than 20, it is usually more appropriate to use a one-to-one correspondence. For larger numbers; however, you may find it better to use intervals [increments] of 10, 25, 100, or 1000 based on the data being graphed. It is important to ensure that the interval in your data display is consistent. For example, if they are creating a bar graph that has a scale with an interval of 2, all of the numbers need to increase by 2 (2, 4, 6, 8, 10, 12 … and not 2, 4, 6, 7, 8, 9, 10, 12…). Depending on the data and the scale that is selected, it may become necessary to create partial symbols and bars that fall between numbers.
A bar graph is a graph that compares amounts in each category to each other using bars. This video shows how to read and interpret a bar graph.