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So far, we've been focusing on marks and channels and as we have seen,
they are really, really important components of every visualization.
But it's also important to realize that marks and channels are
not the only graphical elements that you typically have in a visualization.
There are a number of components that I like to call
contextual components that are actually really,
really important and really useful.
If you remove them,
interpreting a visualization gets really, really hard.
So I like to group all these contextual elements into two main sets.
The first one is the set made of legends, labels and annotations.
And the second one is axes,
grids and reference lines.
So let me start from the first group;
legends, labels and annotations.
Why are they important?
Well, they are important because they
enable the interpretation of the graphical elements.
Think about it, if you don't have legends, labels or annotations,
there is no way for you to actually interpret
the meaning of the objects that are presented in the visualization.
Let me give you a few examples.
If I show you I heatmap matrix like this one,
you see there's no labels,
there is no legend,
there's nothing here that actually helps you in
the interpretation of the marks and the channels.
Now if I add some labels,
the labels that explain why these and rows and columns,
now you start understanding some of it.
So you know that in columns we have different regions,
and in rows we have different categories of products.
Okay? This is very helpful.
And if I add a legend,
the element that you see on the top right,
now you also know that the color represents the average profit.
So all in a sudden it becomes much easier to interpret
the meaning of the graphical objects that you see in front of you.
Okay? Let me give you other examples.
So this is a set of timelines.
Okay. Color the timelines.
Once again, there's no x axis with labels,
there's no y axis with labels,
there's no legend, there's no way for you to interpret this.
Now if I add axis,
now you can start realizing and learning what this graph is about, right?
So you can see that on the x axis there are hours of
the day and on the y axis there are number of pedestrians injured.
This is once again the dataset
about vehicle collisions that we used previously in the course.
And so these two elements are very important.
And if I add a legend,
now you know that these different colors actually represent different months of the year.
So without these elements,
it's basically impossible to interpret this graph.
So these are very important elements.
Enrico BertiniAssociate Professor
Cristian FelixPhD. Candidate
