Charts & Graphs
Guilford County SciVis V104.04
Why Create Charts?
Present the data in a visual method Prevent distorting data Present many numbers in a small space Make large data sets coherent Encourage the eye to compare different pieces of data Reveal the data at several levels of detail, from a broad overview to the fine structure
Bar Chart
Bar graphs are used for comparing items that are not dependent on each other. Bar graphs shows comparisons between unrelated variables. Bar graphs are frequently used to compare multiple entities or to show how one or more entireties vary over time.
Bar Charts
Each column represents a data element, and a complete set of columns makes up a data set. Bar graphs generally have one linear scale on the vertical axis, and a category or sequence scale (such as a time scale) along the horizontal axis.
How to enter Bar Chart Data
Bar Chart
BAR CHART
Population of Different Sample Plots
plot 6
plot 5
plot 4
plots
plot 3 plot 2 plot 1
0
10
20
30
40
50
60
70
Population size in individuals
How to enter Column Chart Data
Column Chart
COLUMN CHART
Populations of Different Plots
70
60
50
Population size in individuals
40
30
20
10
0 plot 1 plot 2 plot 3 plot 4 plot 5 plot 6
plots
For a column chart, the x-axis lists the different categories, and the height of each category's column (with respect to the y-axis) shows the value.
Stacked Column
COLUMN CHART
Populations of Different Plots
70
60
50
Population size in individuals
40
30
20
10
0 plot 1 plot 2 plot 3 plot 4 plot 5 plot 6
plots
For a column chart, the x-axis lists the different categories, and the height of each category's column (with respect to the y-axis) shows the value.
Line (x,y) Graph
Used for related variables and relationships over time. Unlike bar charts, where the differences between the points are the main interest, in Line graphs, it is the similarities that are interesting. Line graph are good for showing trends of continuous data, usually involving time. An area chart is a line chart with the area between the line and the x-axis is shaded.
How to enter Line Chart Data:
Line Graph
LINE GRAPH
Temperture Changes
35
30
25
Temperature in Celcius
20
15
10
5
0 12:00 PM 1:00 PM 2:00 PM 3:00 PM Time 4:00 PM 5:00 PM 6:00 PM
How to enter Area Chart Data
Area Chart
Pie Chart
Pie charts are used for showing parts of a whole or percentages. Pie charts compare the parts of a set to each other and to the whole. The angle or the area of each slice (sometimes called a segment or wedge) is the same percent of the total circle as the data it represents.
How to enter Pie Chart Data
Pie Chart
Play Basketball 8%
PIE CHART
How I Spend My Day
relax 8%
Watch TV 8%
Do Homework 12%
Eat 8%
School 28% Sleep 28%
Scatter Plot
A scatter plot is used to get a visual representation of the relationship or correlation between two variables using the x-y graph method of plotting. Usually the lines connecting the data points are not connected.
Scatter Plot
SCATTER PLOT
Average length of hair in females 16
Length of hair in inches
8 90 95 100 105 IQ 110 115 120 125
Histogram
Histograms are bar charts that display frequencies or relative frequencies in the form of contiguous (touching) bars. Histograms can be used to see the shape of the distribution and to determine whether the data are distributed symmetrically.
Histogram
HISTOGRAM
How to Create a Histogram
Enter your data in Column A. Here I have a set of grades from a class.
Enter the Bin Data
The Bins are the categories into which you are going to place all of the data in column A. In this case the Bins are the Grade Scale.
Add the Analysis Toolpak
Go To Tools – Data Analysis
Select the Input Range
Select the Bin Range
Select the Output Range
Select the Range Data
Select the Chart Wizard
Double-Click One of the Columns
Set Gap Width to 0.
Your Histogram
Bar Chart or Histogram?
Situation We want to compare total income of five different people. Bar Graph or Histogram? Bar graph. Key question: What is the revenue for each person?
We have measured revenues of several people. We want to compare numbers of people that make from 0 to 10,000; from 10,000 to 20,000; from 20,000 to 30,000 and so on.
Histogram. Key question: How many people are in each class of revenues?
We want to compare heights of ten basketball players on a team.
Bar graph. Key question: What is the height of each player?
We have measured several players. We want to compare numbers of players that are from 5-5.5 feet high; from 5.5-6; from 6-6.5 and so on.
Histogram. Key question: How many players are there in each class of heights?
Parts of a Chart
General Guidelines to Follow:
Keep graphs simple -- make the data do the talking. Don’t "liven" up you chart with extra colors, 3D, or pictures. Interesting data captures an audience’s attention more than any graphic or special printing effect could. Use meaningful titles and labels -- let the audience think about what the data means, not what the data is or could be. Be truthful with the axes -- Do not exchange scales or perspectives to gain a falsely perceived advantage
Why Not 3D?
3D may NOT be a good idea because the data may appear distorted, can be misinterpreted, or may be misleading.