Graphs and Charts
Contents
    Graphs and Charts

Section:
    Graphs and Charts

Most spreadsheet programs have features designed to help you create graphics from your data. These graphics can help you to illustrate the meaning of the numbers on the chart. They can also be used to stimulate interest, since graphs are often easier to read and understand than a bunch of numbers. Graphics can also be used to help make a point. A well - designed graph can do much to illustrate an idea. Graphs are commonly used in business and scientific settings to illuminate the meaning of spreadsheet data.

Subsection(s)

  • Parts of a graph
  • Types of Graphs
  • Misleading with Graphs
  • Parts of a graph

    There will be a few key elements to any graph.

    Data Range
    The graph is a graphical interpretation of some data. Generally, you will create a spreadsheet that generates some type of data, and use the graph to illustrate the data. When you define a graph, you will need some way to explain which data is being depicted. You can usually select the data you want with a range.

    X and Y axes
    As you may remember, the X axis is the stuff that goes along the horizontal border of the chart. The Y axis is the vertical stuff. Most spreadsheet programs try to guess which stuff you want plotted as the X axis and which you want as the Y axis. If the graph looks completely wrong, you might want to look for some kind of feature that allows you to change the X - Y orientation.

    Upper and Lower Bounds
    You might want to specify the upper and lower limits of the axes. The program will usually try to guess what you want, but you may still need to modify it.

    Labels
    There will usually be an option for setting or changing the labels on a graph. This will allow you to put informative (or misleading, I guess) labels on the graph to make it easier to read. (unless you are sneaky.)

    Graph type
    You will usually get some type of option to change the type of graph that is displayed. See below for more information about graph types.

    Types of Graphs

    There are a number of major styles you can choose from when creating a graph. The style you choose implies some things to your readers.

    Area Charts
    Area charts show the relative contributions over time that each data series makes to a whole picture. For example, an area chart would be good to show how much the relative amounts of the principal and interest change over time of a mortgage.

    Bar Charts
    Bar charts compare distinct items or show single items at distinct intervals. Usually, a bar chart is laid out with categories along the vertical axis and values along the horizontal axis. In other words, the bars are horizontally placed on the page. Bar charts are useful for comparing data items that are in competition, so it makes sense to place the longest bars on top and the others in descending order beneath the longest one.

    Column Charts

    Column charts are like bar charts because they compare distinct items or show single items at distinct intervals. However, column charts have the categories arranged along the horizontal axis and the values along the vertical axis, so the bars are vertical on the chart.

    A very common use for column charts is to display how values change over discrete units of time (monthly or yearly change, for example).

    Line Charts
    a line chart plots the value of the variable as a specific point, then 'connects the dots' in order to give you some idea of the relationship of consecutive points.

    Line charts may also be used to show how the value of a variable changes over time. Unlike bar and column charts, line charts imply continuous change rather than a number of discrete points. For this reason, line charts are better at implying a trend. For example, if you are doing an experiment about the number of fish in a certain pond, you might be interested in the number of fish in the pond at a certain time, but you may also be very concerned with the trend of the fish population. Is it increasing or decreasing?

    Just because a line chart implies trends does not necessarily mean they are there! Be careful when interpreting such charts that you do not automatically assume intermediate values by the line placement.


    Pie Charts

    A pie chart is used to show proportions of a whole. It is very useful for figures that relate to a larger sum, such as demographic data or budget information. It is easy to get a feel for the relationship between component values when they are placed in a pie chart. Be careful that you do not have too many slices in the pie, or they will become meaningless.

    Also, note that a pie chart is usually used as a snapshot of ONE moment in time. If you want to show relationships as part of a whole over time, you would use an area chart. If you want to look at a number of pie charts at once, you might consider a doughnut chart. (look it up in online help or just play around with it!)

    Scatter Plot
    A scatter plot is the simplest type of graph. It simply plots the data points against their values, without adding an connecting lines, bars or other stuff. This is visually the least appealing type of graph, but the lack of bells and whistles can actually be an advantage. Since all the other types of graphs tend to have some kind of psychological implication built in (eg bar charts imply comparison, line graphs imply continuity), scatter diagrams are devoid of this type of clutter. If you are searching for the patterns and meaning in a graph, you may find the scatter diagram the clearest representation of the data. Once you understand what it means, you can use one of the other types of graph to give your readers whichever impression you choose.

    3-D Charts

    Many of the above charts can be created in 3-dimensional forms. The charts work pretty much the same way, but they can be a little more complex to work with. A three dimensional chart can be rotated so that it can be seen from other perspectives. 3-D charts are often used for the added dramatic impact they provide to a presentation.


    Misleading with Graphs

    Graphs can send a very powerful message to people. The use of images makes a much more vivid impact that straight numbers. Graphs also have the capability to strengthen implications about data based on the type of graph, colors used, and other tools. Just because you see a graph does not mean you should believe it. Examine carefully where the data came from, and what it is telling you.

    It is possible to make exactly the same data appear to have completely different meanings. Examine the figures below for an example:

    If you look carefully, you will note that the graphs are both showing exactly the same thing, but by careful manipulation of the graph sizes, axis scales, and titles, the two charts appear to have exactly OPPOSITE meanings.


    Bill Dueber