Introduction to Graphing
The Island of Krakatau
In 1883 the island of
Krakatau experienced a
violent volcanic eruption.

The island was destroyed!
All life was killed.
What Has Happened Since
1883?
Year (x)
# Species (y)
1883
0
1908
13
1920
28
1950
34
1985
38
This table shows the data that
was collected over the 100
years following the eruption.

Each row shows a year and the
number of species of birds that
were observed on the island.
What Else Can We Do With the
Data Table?
Scientists look for trends in
data & then attempt to
explain those trends.
Scientists use GRAPHS
to make it easier to see
trends in data.
Year (x)
# Species (y)
1883
0
1908
13
1920
28
1950
34
1985
38
I.D. Parts of a Graph
Graph Title:
The title of the graph should tell the
reader what data is being
represented.
Always read the title of a graph
BEFORE looking at any other data!
I.D. Parts of a Graph
Y-axis:
The vertical axis along the left is
called the Y-axis. Number of
species is represented along this
axis.
The lower value on the Y-axis is O
and the highest value is 40.
I.D. Parts of a Graph
X-axis:
The horizontal axis along the
bottom is called the X-axis.
Years are represented along this
axis.
I.D. Parts of a Graph
Origin:
The point where the X and Y axis
meet is called the ORIGIN.
It is the smallest value a point can
have on the graph for both axes.
More on the X and Y Axes
The X and Y axes identify your
experimental variables.

Independent Variable (I.V.)
Goes on the X-axis (horizontal)

Dependent Variable (D.V.)
Goes on the Y-axis (vertical)
Data Table Review
Independent Variable:
The I.V. if found in the left
column of your data chart.
This information is placed on
the x-axis.
Year (x)
# Species (y)
1883
0
1908
13
1920
28
1950
34
1985
38
Data Table Review
Dependent Variable:
Year (x)
# Species (y)
The D.V. if found in the right
column of your data chart.
1883
0
This information is placed on
the y-axis.
1908
13
1920
28
1950
34
1985
38
Graph this Data
Year (x)
# Species (y)
1883
0
1908
13
We are going to graph this
data in your notes
together.

1920
28
1950
34
1985
38
This graph is going to be a
line plot of the data set.
Each point will represent one
row of the table.

We will start with row 1.
Row Two of the Data Table
Year (x)
# Species (y)
1883
0
1908
13
1920
28
1950
34
1985
38
Row Three of the Data Table
Year (x)
# Species (y)
1883
0
1908
13
1920
28
1950
34
1985
38
Row Four of the Data Table
Year (x)
# Species (y)
1883
0
1908
13
1920
28
1950
34
1985
38
Row Five of the Data Table
Year (x)
# Species (y)
1883
0
1908
13
1920
28
1950
34
1985
38
Double-Check Your Work!
Why Connect the Dots?
The connecting lines allow you to visualize
the trends in the data.
Which statement below BEST summarizes the trend shown
by the graph?
A.
Land birds have been unsuccessful at colonizing the
Krakatau islands since the 1883 eruption.
B.
Colonization by land birds has steadily increased the
number of species since the 1883 eruption.
C.
Land birds colonized the islands immediately after the
eruption, but the number of species has steadily
decreased over the past century.
Good Graphing Checklist
Does your graph have a title?
Have you placed the independent variable
on the x-axis and the dependent variable
on the y-axis?
Have you labeled the axes correctly and
specified the units of measurement?
Is your data plotted correctly and clearly?
Graphing Practice
Make a line graph of the data below:

pH of Water
Number of Tadpoles
8.0
7.5
7.0
6.5
6.0
5.5
45
65
70
80
40
20
Refer back to your Good Graphing Checklist.
Effect of pH on Tadpole Populations
Graph Title?
70
60
50
40
30
20
Independent
Variable?
pH of Water (x-axis)
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
10
4.0
(y-axis)
of Tadpoles
Numbers
Variable?
Dependent
80
What is the independent variable?
What is the dependent variable?
What is the optimum pH for tadpole
development?
Between what two pH readings is there the
greatest change in tadpole number?
How many tadpoles would you expect to find in
water with a pH reading of 5.0?
Identify the Graph that Matches the Story…
I had just left home when I realized I had forgotten my
books so I went back to pick them up.
Identify the Graph that Matches the Story…
I started out calmly, but sped up when I realized I was
going to be late.
Identify the Graph that Matches the Story…
Things went fine until I had a flat tire.