1. 2. Graphing
Sci. Info Skills

2. Graphing
Remember the cliché about pictures and thousands of words (or numbers)
But only if the picture is clear and accurate
Hand-drawn graphs are slow, inaccurate and unprofessional

3. Rules for preparing graphs
axes labelled clearly
informative title
axis scale is the same all the way along
the axis scales must be shown
where multiple series are plotted on the same graph, make it clear which data belongs to which line/column (legend)
don’t overdo the fancy formatting
the measured variable should be plotted on the vertical axis

4. Formatting issues - General
Do not accept the default settings without thinking “can I make this look better?”

5. Formatting issues - General
2D vs 3D
“3-dimensional” columns look better than plain rectangles
they make it more difficult to judge where the top of the column is
gridlines can help
avoid 3D piecharts completely

6. 2D column graph

7. 3D column graph

8. Formatting issues - General
Gridlines
too many gridlines definitely mask the graph
Excel seems to default to 10 often (too many)
definitely needed with 3D column graphs
less necessary with 2D columns
not needed at all with scatter graphs

9. 3D without gridlines

10. 3D graph with default gridlines

11. 2D without gridlines

12. Formatting issues - General
Legends
crucial where there are more than one data series
totally useless when there is only one
made useless if the labels are simply Series 1, Series 2 etc

13. Useless legend

14. Useless without a legend

15. Useless with one

16. Formatting issues - General
Background
the default is mid grey
hopeless when printed
change to white or none
some colour on Powerpoint with non-white background

17. Dark slide – no background

18. Dark slide – white background

19. Dark slide – non-white bkgd

20. Formatting issues - General
Colours & patterns
don’t change colours and end up with similar brightness
bright light colours are hard to see on PPt
avoid patterns

21. Hard on the eyes!

22. Excel chart types look at the graph and ask yourself:
Does this graph tell me what I want it to?
Column, bar, cylinder, cone, pyramid
plotting frequencies for category data
only difference between them is appearance
personal preference

23. Excel chart types
Line
Only useful for plotting frequencies for tallied numerical data
where a XY scatter doesn’t work (eg group values on horizontal axis)
MUST NOT be used for category data
Pie & doughnut
show relative proportions of different categories
doughnut allows multiple different sets to be compared

24. Excel chart types XY scatter
numerical data where two variables have some relationship to each other
eg concentration vs time, temperature vs CO2, absorbance vs concentration
Area
line graph where the space underneath is filled with a solid colour
can be used for multiple related sets

25. Excel chart types Radar, bubble, stock
limited or no use in this context
Line-Column
allows a combination of each type

26. Column type Class Exercise 2.1
Does either of the above graphs illustrate the data better? No

27. Column types – multiple sets
multiple column/bars per category

28. Column types – multiple sets
stacked columns
gridlines useful here

29. Exercise 2.2 Which multiple set way is better at portraying the data?
each gives different way of comparing
multiple columns gives easy comparison of each category
stacked gives an overall picture of how they differ

30. Alternative multi-column - OK

31. Alternative stacked – wrong!
Exercise 2.3
What’s wrong?
There is no
reason to stack
urban &
undeveloped
on each other;
they don’t belong together

32. Formatting issues - Columns
your choice of which style
is 3D a plus or minus?

33. Line graphs easy to see line and scatter charts as the same thing
line charts are basically for the same type of data as column type graphs
must not be used for category data
only tallied numerical data

34. Line graph - OK

35. Exercise 2.4
How does the line graph compare to the column/bar graphs for this data?
no better or worse
the line implies continuity between the values on the horizontal axis which is fine

36. Exercise 2.5 Why is a line graph wrong for plotting category data?
Because it implies a connection between the categories

37. Scatter graphs both axes need a number associated with them
two measurements should have been made about that particular item
eg absorbance and concentration, pH and time
if there is only one measurement, it is not possible

38. Scatter graph – line or dots
line or dots or both?
line – if there is an obvious connection between the points
eg the measurements have been made at different times or at different distances, but on the same basic population
dots only – no direct connection
join-the-dots line – no need to show the dots
best-fit line – must show dots

39. Scatter graph – line, no dots

40. Scatter – dots only

41. Scatter – line & dots

42. FORMATTING ISSUES – Scatter graphs
make sure the line is thick enough to be clearly visible.
if you have more than one line on the graph, make sure that:
they differ in style (solid, dotted, dashed)
are not light colours, to ensure it is readable when printed
when using join-the-dots, avoid auto-smoothed line

43. Bad scatter graph

44. Good scatter graph

45. Pie charts for category data to show the relative proportions
similar to stacked column
only used when items are from the same population
eg amount of each type of recyclables in collected waste
not suitable for related items from different populations
eg weight of paper collected in recycling in different suburbs
inappropriate to leave out some categories

46. Pie chart

47. FORMATTING ISSUES – Pie charts
do not use 3D pie charts under any circumstances
If you intend to print it out in monochrome, be careful to avoid adjoining segments of the same colour intensity
the labels next to the segments, rather than in a box-type legend
not necessary to include values and especially percentages in the label.
to emphasise a particular category, it is common practice to draw that segment slightly displaced from the main pie

48. Assignment 3 graphing provided data (2 separate data sets)
some graphs are specified format, other not
evaluating which graph works better for given data