Multi Series  Graph

Graph can be used to display complex stories. A single graph can sometimes be used to display complex stories elegantly but frequently it will not do . So we will cover two useful way to show this complex stories .

1)Combine multiple unit of measure

we use single graph to display multiple quantitative variable when they all use same unit of measure .but if the value of variable differ by large amount then problem occurs , cause low values to look relatively flat.

Fig…11.1

When you wish to display two units of measure for the purposes of the comparison, the best way to avoid confusion is usually to use two separate graph rather than a single graph with two Quantitative scales. Unless you are certain that your readers are comfortable with dual-scaled graphs, it is best to avoid them.

 Fig…11.2, .3(Focus on the intersection)

2)Combining multiple graph in a series

In 2D graph, we can squeeze the data to a certain limit but we have a solution to display multiple measures(more than 2) in 2D : multiple graphs arranged together as a series(Trellis chart -A series of graphics , showing  the same combination of variables , indexed by changes in another variable.)

Fig 11.4  (Focus on adding more than two series).

When you need to add one more variable (i.e., another set of  categorical subdivision) to a graph , but you have already used all the practical means to visually encode in it, you can do so by constructing a series of related graphs , in which each graph in the series displays a difference instance of the added variable. Avoid 3D graph and involves multiple graphs arranged in a series so that it will be easily

compared .

Notes : As the number of graph grows , the trick is to reduce their individual size enough to allow them to be seen together . You can arrange the graphs horizontally and vertically , or in both directions to produce a matrix arranged in  multiple columns and rows, redundant labels should be eliminated .

Best practices

Consistency            

Consistency is required for the comparison. Knowledge of first graph in a series guides you through rest. Consistency in visual includes:

• Aspect ratio of the axes
• Color used to encode data .
• Font etc.,

Graphs in a series of small multiples should be consistently designed with only one exception : text used for the labels , titles , or legends does not need to appear redundancy in each graph .

Pay particular attention to the scales along both axes  fig..(11.6)

Categorical scale also remains consistent with the same items in the same order and the same full list of items even when a value is zero or null. (fig 11.7) 

Arrangement 

Before arrangement we should answer this question :  which items do you want to make easiest for your user to compare ? And then arrange the graphs in a series of small multiples in the way that makes it as easy as possible to focus on and compare the values that are the most relevant to your reader`s interests.

Sequence

If the index variable has an intrinsic order , you should sequence the graphs in this order unless you wish to display a ranking relation .Otherwise , rank the graphs in order based on a quantitative measure associated  with the index variable.

Rule and grid lines

Only use rules or grid lines between graphs in a series when either of these two conditions exists:-

• The graph must be positioned so closely together that white space alone cannot be adequately delineate them .
• The graph are arranged in a matrix and are positioned so closely together that white space alone cannot adequately   direct your readers to scan either across or down in the manner you intend.