Graphics Reference
In-Depth Information
Captions, Legends and Annotations
Ideally, captions should fully explain the graphic they accompany, including giving
the source for the data. Relying on explanations in the surrounding text rarely works.
Ideals cannot always be met and very long captions are likely to put off the reader,
but the whole point of a graphic is to present information concisely and directly.
A compromise wherethe caption outlines the information in the graphic and a more
detailed description can be found in the text can be a pragmatic solution. Graphics
whichrequireextensive commentary maybetrying topresenttoomuchinformation
at one go.
Legends describe which symbols and/or colours refer to which data groups. Tute
recommendsthatthisinformationbedirectlyontheplotandnotinaseparatelegend,
so that the reader's eyes do not have to jump backwards and forwards. If it can be
done, it should be.
Annotations are used to highlight particular features of a graphic. For reasons of
space there cannot be many of them and they should be used sparingly. hey are
useful for identifying events in time series, as Playfair did (Playfair,
), or for
drawing attention to particular points in scatterplots.
UnionestimatesofprotestturnoutinFig.
.
arelargerthanthepoliceestimatesby
roughly the same factor, except for the two extreme exceptions, Marseille and Paris,
where the disagreement is much greater.
Positioning in Text
Keepinggraphicsandtextonthesamepageoronfacingpagesisvaluableforpractical
reasons. It is inconvient to have to turn pages back and forth because graphics and
the text relating to them are on different pages. However, it is not always possible to
avoid this. Where graphics are placed on a given page is a design issue.
Size, Frames and Aspect Ratio
Graphics shouldbelarge enoughforthereadertoseetheinformation inthemclearly
andnotmuchlarger.hisisaroughguideline,asmuchwilldependonthesurround-
ing layout. Frames may be drawnto surround graphics. As frames take up space and
add to the clutter, they should best only be used for purposes of separation, i.e. sep-
arating the graphic from other graphics or from the text.
Aspect ratios have a surprisingly strong effect on the perception of graphics. his
is especially true of time series. If you want to show gradual change, grow the hor-
izontal axis and shrink the vertical axis. he opposite actions will demonstrate dra-
matic change. For a scatterplot example, see Fig.
.
, which displays the same data
as Fig.
.
. here is useful advice on aspect ratios in Cleveland (
), especially the
idea of 'banking to
degrees' for straight lines.
Colour
Colour should really have been discussed much earlier. It is potentially one of the
most effective ways of displaying data. In practice it is also one of the most di
cult
to get right. A helpful check for colour schemes for maps, Colorbrewer by Cynthia
