2. Graphing Sci. Info Skills

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

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

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

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

2D column graph

3D column graph

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

3D without gridlines

3D graph with default gridlines

2D without gridlines

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

Useless legend

Useless without a legend

Useless with one

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

Dark slide – no background

Dark slide – white background

Dark slide – non-white bkgd

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

Hard on the eyes!

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

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

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

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

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

Column types – multiple sets multiple column/bars per category

Column types – multiple sets stacked columns gridlines useful here

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

Alternative multi-column - OK

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

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

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

Line graph - OK

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

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

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

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

Scatter graph – line, no dots

Scatter – dots only

Scatter – line & dots

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

Bad scatter graph

Good scatter graph

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

Pie chart

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

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