|
Microsoft does not know a heckuva lot about presentation design,
but one thing they do correctly in PowerPoint is to make
available different types of graph so that you can match the
graph type to the point you’re trying to make with your data.
There are twelve different graph types available with
PowerPoint 2000, but few of those styles work well in the
low-resolution world of computer-based presentations. With few
exceptions, here is how you want to use the following types:
• Pie
Graphs for Share
• Bar Graphs for
Comparative Amounts
• Line Graphs for
Trends, Time
Pie Graphs
Pie
graphs (commonly misnomered pie charts)
are one of the more overused, and hence misused, types of
graphs, primarily because they are so easy to make, and easy to
make look good. They
are misused when chosen to show amounts rather than share.
The beauty of pie graphs is that they show so clearly
what they are supposed to show, i.e., how much of the whole each
element contributes. In
most cases the actual amounts – in this case percentages –
are actually secondary to the area of the slices in terms of
telling the story.
When you look at a pie graph with five or fewer slices,
your brain can quickly ascertain which groups dominate.
We often see pie graphs with more than 5 elements, but
they then become more difficult to comprehend in short order.
In most cases, consider whether your story needs to
include details about all the players, or whether a group of
insignificant contributors can be grouped as “others”.
If
you want to show how much volume
each element contributes, rather than what fraction,
you’ll want to use a bar graph.
Bar Graphs
To show relative sizes of different segments as well as
the actual amounts, you’ll want to use a bar graph.
Bar graphs are designed to show volumes against a y-axis
that clearly delineates the units of measure.
By having a series of bars next to each other, we can see
how each element compares with the others as well as what
absolute volume the element represents.
There are variations on the bar graph, such as a stacked
bar, where different elements are stacked on top of each other
to form a series, or a 100% bar graph, where all the bars are
the same height but are split to show what percent of the whole
the volume reflects. In a presentation environment, esoteric
options are best to be avoided.
Line
Graphs
Line graphs have the unique advantage of speaking to
inherent right-brain prejudices about information.
That is, when typically conditioned western minds see a
graph with no labeling, they automatically assign “volume”
to the y-axis, with “up” meaning “more”, and a time-line
to the x-axis, with the left side meaning most recent. Just as we read from left-to-right, rightward motion
subconsciously means positive motion.
You would want to use a line graph, then, to show a
progression in amount from one point in time to another.
The elevation of the line at any one point represents the
quantity of the tracked data at that moment.
Audiences, wanting to be the first-to-know, will
automatically make assumptions about the types of values x-axes
and y-axes represent. Don’t
disappoint them.
Data labels
Graphs are a great way of making complex information
easily understood. But
graphs work best only when you properly integrate words, numbers
and images. Whenever
possible, label the elements of your graph directly on the
elements themselves, rather than relying on the ever-popular
clarity killer, the legend. Legends require too much effort on
the part of listeners to discern exactly what each data point
is. Just be certain your labels don’t clutter up the otherwise
clear “picture” a good graph can make.
If
you have a number of graphs in your presentation, you’ll want
to avoid dumping a data overload on your audience by
over-labeling each one. In
fact, in many cases you can tell your story forcibly enough by
only the size of your data elements, without burdening their
minds with numbers that they’re likely to forget by the end of
the presentation. However,
it’s also not a bad idea to have what we call “reference
slides” that do contain all
the data attached to the end of your main slide deck.
To really impress your crowd, install hyperlinks to these
slides from the ones in your main show, and when some
vice-president makes a stink about wanting to know the whole
story, zap to your total-info slide and give him what he wants.
He probably won’t ask again.
|
