Graphing in Mr. Gentry’s Room

Why graph? Visual representation of data We plot data so that we can more easily observe trends or behavior of the data Graphing is a common method of data analysis.

Basics there are two axes - horizontal (x-axis) and vertical (y-axis) a point on the graph is denoted by an ordered pair (or coordinates (e.g., (3,8)) where: the first number refers to horizontal position on the x-axis, the second number refers to vertical position on the y-axis, sometimes the ordered pairs are listed in tabular format with headings that correspond to the labels on the axis the two axes intersect at point called the origin with coordinates (0,0)

Keep in mind: Eliminate the need for any guesswork from the reader. Choose the proper graph to display what you need to show

Line Graph Line graphs are used to track changes over periods of time. Line graphs can also be used to compare changes over the same period of time for more than one group.

Line Graph X-Y Plot X-Y plots are used to determine relationships between the two different things. The x-axis is used to measure one event (or variable) and the y-axis is used to measure the other. If both variables increase at the same time, they have a positive relationship. If one variable decreases while the other increases, they have a negative relationship. Sometimes the variables don't follow any pattern and have no relationship.

Bar graph Bar graphs are used to compare things between different groups or to track changes over time. However, when trying to measure change over time, bar graphs are best when the changes are larger.

Pie Chart Pie charts are best to use when you are trying to compare parts of a whole. They do not show changes over time.

Class Graphing Rules Origin (0,0) is lower left corner of graph Proper location/orientation and use of the x and y axis Proper complete label of axes including units Correct type of graph(line, bar, etc) – match to data and what you are trying to study or show

Graphing Rules Neat, aligned, legible Use of graph paper Sometimes ok to use your lined paper if you measure accurately and consistently.

Graphing Rules Appropriate scale No inconsistent scale No line breaks No squiggly or jagged lines to represent change in scale

I commonly run into the problem of students misunderstanding the construction of a meaningful plot when I teach them about topographic profiles. When a student comes to me with questions about how to construct this type of plot, I walk them through the thought process of labeling axes and deciding on scale: First, what are we trying to represent here? Then, decide what the axes are...horizontal distance (in miles or km) on the x-axis and vertical relief (in feet or meters) on the y-axis. Next, determine the range of elevations present along the cross-section of interest Show credits Hide Image showing construction of a topographic profile from the USGS Learning Web. Now, we need to determine the increments along the vertical scale. We can do that by thinking about several important things: What is the contour interval? Increments similar to contour interval may be helpful. How many possible increments are there on your paper? If the difference in elevation is 480 ft. and there are 10 increments on the plot, should you plot in increments of 48? Based on your contour interval, is this reasonable? Would it be easier to plot increments of 50? Finally, plot the elevations in the appropriate places on your graph and connect the dots with a SMOOTH curve. In the end, students seem to be able to relate to wanting something to be easy to read and, in the process, begin to learn about making realistic choices.