7.1: Types of Graphs
Line graphs: Line graphs are commonly used in the water and wastewater industry. They are quick and easy to create and read. It is important to read the labels on the horizontal and vertical axes and to read the graph from left to right. To read information on a line graph, locate a point on the line graph, find the corresponding value on the horizontal and vertical axes.
Bar graphs: A bar graph can consist of vertical or horizontal bars that can display numerical or categorical data. To read a bar graph, for each category, locate the height (or length) of the bar and read the scale or value. Some bar graphs will consist of double bars or multiple bars for each category. This allows information to be compared at a quick glance.
Pie charts: A pie chart is generally used to show percentages or proportions of categories as they relate to each other. Each wedge in a pie chart represents a category and the size of the wedge represents the percentage or proportion of that category.
Semi-log or log-log graphs: A semi-log graph has logarithmic scales on one axis and a numeric scale on the other axis. A log-log graph has logarithmic scales on both the horizontal and vertical axes. They can be used for showing the flow rate.
When reading a graph, be sure to pay close attention to the scale of the axes and/or picture. The markings on the axes or picture indicate the size of the numerical values depicted on the graph.