How to draw scientific diagrams
by Chris Woodford. Last updated: August 24, 2014.
No-one's ever likely to mistake me for
Michelangelo, but I have at least one
thing in common with that famous Renaissance artist: both of us have
used art to communicate important things to other people. In
Michelangelo's case, it was stunning paintings and sculptures; my own contribution
to art history has been far more mundane: over the last decade or
two, I've had to produce dozens of diagrams to illustrate the books
and web pages I've written about science and technology.
Much of the time I've had superb artists and illustrators to help: I've just roughed out a basic
sketch and they've done all the clever stuff for me. Recently, since I've been
writing more for the web, I've produced most of my own art as well, which
means I've had to learn to draw scientific and technological things far better than ever before.
That's been a real challenge, because I've never been good at art. Fortunately, scientific art is
very different from real, artistic art and, even if
you've as little artistic talent as me, you can still do a passable
job of communicating your ideas if you use a decent computer graphics package.
So what's the secret? Here are some of the tips I've picked up over the years that I'd like to share with you now.
Artwork: How electricity works: I've redrawn this diagram at least four times in the last few years and this will probably be the final version. It was drawn large and scaled down to make the battery look good. I've put a big caption in the center of the picture and labeled the three key components. The drawback of doing this is that readers who don't use English, but who use auto-translation to read my pages in their own language, will see English text they may not understand. I discuss an easy way around this in point 6 below.
1. Keep it simple
Once you've decided what you're going to draw (say, how a television
works), strip down to the absolute essence of what you're trying to
communicate (the process by which a broadcast signal arrives and is
turned into a picture and sound by the circuits inside). If this is
the kind of thing you're trying to explain, you don't need to show
every single electronic component: just pick the handful of key
bits that tell your story and forget everything else. Combine
components and show them as bigger, cruder parts if you wish. Good
how-it-works diagrams have maybe only a dozen distinct elements to
them at most.
Remember that your entire explanation doesn't have to rest on
this one artwork: you'll have text and you can add photos too to show finer details
of how things appear in reality. If you're going to use photos and artworks together, it's
best to choose the photos first so you can draw your artwork to relate
to them in some way (you could copy key details from the photos, or use the same
colors for parts that the photos show so your readers can relate the
artwork directly to the photos without difficulty).
Photo: How a television works: This diagram illustrates many of the principles I've set out in this article. It's ultra-simplified, there's no excess decoration, I've removed everything but the components I want to explain
(fewer than 10 in total), I've arranged the internal parts in an order that makes sense to my explanation (taking lots of licence), I've made the artwork flow logically from top to bottom and from left to right, I've mixed photography (of the chip and speaker) with drawing, and I've left the text off the artwork (in favor of numbers) so the captions will translate properly. It's no Michelangelo, but I think it does its job well.
2. Communicate not decorate
There's a great temptation to draw things in extreme detail so they look as
realistic as possible, but there's usually no need: the fewer lines
you use and the simpler you make things, the easier they are to
understand. If you're drawing the drive mechanism of a car, and
explaining how power gets from the engine to the
wheels to make it go
down the road, you don't need to draw any of the parts in any great
detail. You can just draw the car wheels as circles, for example—you
don't need to draw the nuts on the hubs or the tread on the tires!
3. Take artistic (and scientific) licence
Painters often use what's called "artistic licence," which means they
don't slavishly follow reality if they can make a better picture some
other way. They might put in extra people, move trees, draw buildings
in different places, and take all kinds of other liberties with
reality to produce a more interesting composition. As a scientific
artist, you should feel free to do exactly the same. Leave things out
if they complicate what you're trying to communicate; add extra
things in if they help. If it confuses to draw things exactly as they
are, draw them a different way. Your number one priority is not to
depict reality exactly as it is—you can use a photograph for
that—but to help people understand something. Remember all the time that
you are trying to communicate clearly; it's fine to bend the truth a little to make that happen.
4. Go with the flow
In the western world, we read pages of text from left to right (Arabic
readers are used to their eyes working in the opposite direction) and from top to bottom. People
naturally try to read diagrams the same way, starting on the left and
moving to the right, and flowing from the top of the page to the bottom, so design your artworks that way
if you possibly can. If you're laying out the parts of something, assume they'll be read left-to-right
and top-to-bottom. If you're illustrating a sequence of things, arrange it in a logical
order with the first item on the left, then the second item, and so
on... working your way across to the right of the page.
5. Number in a logical order
You'll often find it helps if you number items on a diagram, especially if
you're showing a definite sequence of things or lots of different
parts. Again, if you're going to do this, make sure the numbers flow
logically either from left to right, top to bottom, clockwise, or
anticlockwise. Don't have the numbers jumping around all over the
place (especially if there are lots of them). Readers don't want to have to keep scanning their eyes back and forth over
the diagram to search for the next item: make it easy and less confusing by putting things in the order they expect.
6. Leave text off the artwork on web pages
Often you'll need to label a diagram with names of parts or short captions
that explain what's going on. If you're preparing a diagram for a
book, it's usually easiest to put the text on the diagram itself—and
there's no real reason for not doing so. If you're producing an
online diagram to illustrate a web page, there's something else to
think about. If your website is like mine, a high proportion of your
readers may be reading your pages not in English but
auto-translated into their own language.
If you write text on your artwork (as I've done in the top
picture on this page), foreign language readers may not be able to
understand it. The alternative (and one I've used on the other artworks shown here)
is to put numbers on my pictures and then caption those numbers
in the HTML text of the web page, in something like a numbered list. Then
if the web page is auto-translated, the captions will be
auto-translated too and readers will still be able to understand the
artwork properly. The broader lesson here is to see things through your
7. Explain in space... and time
Often you'll want to explain how something like a machine works in a
sequence of distinct steps. Sometimes you can do that by drawing the
parts inside in a particular way (not necessarily how they're
arranged in reality), laying them out on the page (or the screen)
from left to right and numbering them so you can describe what they
do in the correct order. That's what I've done with the TV set and airbag
artworks on this page. I've separated key parts in space to make a process clear
in each case.
If you're drawing something for the web, there's also the option of making a simple animation—which
amounts to separating parts in time as well as space. If you want to do this, the easiest way is to
make an animated GIF, which is simply a series of individual frames (separate pictures) packaged into a conventional GIF file so they play in sequence as many times as you like.
Bear in mind that animated GIFs can turn into very large files, they'll take
time to load, and they may slow down your pages. There are three things you can do to address that:
try not to get carried away with too many frames (four is about the maximum you want); keep the size of
the artwork as small as you can without sacrificing clarity; and use a relatively
limited color palette (a small number of colors). If you find you've ended up with a very big GIF file, try reducing
the number of colors from 256 (typically the default) to 128, 64, or 32. Find a value that preserves
the quality without making the file size too big.
You can also use Flash for making animations, but it's more of a nuisance for users. You can't be certain that Flash files are supported on browsers and mobile devices and, with the development of HTML5, there's some doubt about how long Flash itself will survive. Animated GIFs have been around since the earliest days of the web; they're tried-and-tested and work on pretty much everything.
Photo: How a simple smoke detector works. This one uses two simple, alternating frames to communicate an idea that would be hard to depict without animation. In the first frame,
I show the detector in its passive state; in the second frame, I show what happens when smoke enters and triggers
the alarm. It's easy to make animations like this. You just draw one frame, save it and make a copy, modify that copy to make your second frame, and then combine the two frames in a single animated GIF. You can easily specify how many times the frames loop (here it's indefinitely) and the time lag between them. You can make animated GIFs in lots of different graphics packages, including the GIMP, which is what I use.
8. Scale your pictures according to your users
In the world of Michelangelo art, bigger is often better, but that doesn't
always hold for scientific art. Generally you want diagrams that are
big enough to see and understand. In books, page size and layout are
the constraints you work with. On the screen, things are slightly
different. Bear in mind that not everyone will have a
screen the same size as yours. Increasingly, people are browsing
websites on handheld devices such as iPhones, which have a maximum
screen size of 320×480 pixels. On this website, we're now trying to
keep all photos and artworks within these dimensions if we possibly
9. Beat your poor artistic skills
Picture size is also helpful if, like me, you're a clumsy artist. I
find I always know what to draw, but actually translating what's in
my mind into a nice-looking picture on the screen is quite difficult because I don't have enough
skill with a mouse.
Fortunately, there is a solution. First, figure out the final size of the artwork you want (say it's
300×300 pixels). Then, instead of making your "canvas" that size
to start with, make it at least twice as big (or three times as big
if you can). Draw your picture so everything is double or triple size
and then, when it's finished, scale it down to 300×300 or whatever.
You'll be amazed how much more professional it looks. Your wiggly,
pixelated lines will all look far sharper and better drawn. Bear in
mind that lines will get thinner as you scale a picture down so
you may need to use a bigger "brush" size than you
would normally. Also, text may blur as you scale down so you may want to add
in any text or numbering after the scaling operation, not before.
Another good trick for so-so artists is to mix
photography with drawn artworks, as I have in the TV picture up above. If you need to illustrate bits of
something you can't draw, find copyright-free photos of them online
(or even take your own photos) and cut and paste into your artwork as
necessary. I took photos of the speaker and circuits because I didn't think I could draw them well.
Photo: How an airbag works: I'm really pleased with how this little drawing turned out. The final artwork is 400×300 pixels, but I drew it about three times the size (so the original filled my screen) and scaled it down.
Overall, the effect is far better than if I'd drawn at 400×300 to start with. Not everything worked out, though: after I scaled down, the circuit (3) became too blurred to make out properly, so I had to redraw it. Bear in mind that anything finely detailed will take up a half, a third, or a quarter as many pixels after the scaling process, which could make it difficult to see. Experiment with scaling first so you know what will work and what won't before wasting your time on elaborate detail.
10. Use pullouts instead of cutaways or explosions
If you're drawing technological things, like machines, you often need to
show bits that are hidden away out of view. A really skillful artist
can do this with a cutaway (a composite drawing in which part
of the exterior is removed to show what's lurking behind) or an
exploded diagram (where the parts inside something are
separated in a very logical way that keeps a suggestion of how they
fit together). Cutaways and explosions are very demanding and time-consuming for even
skilled artists to draw, but again there's a solution—in the form
A pullout is simply a detailed, magnified drawing
of one part of another drawing that you place on top with lines to
show what it relates to. (It's a bit like holding a magnifying glass
over part of your main drawing.) One approach is to take a photo of
the object you want to illustrate and draw a large circle on some
part of it where you can safely cover what's underneath. Inside the
circle, draw a simple artwork illustrating some key detail of what's
happening inside the object. Then draw two lines from the outside
edge of the circle that meet at the point on the object where the
action you've drawn is happening. (Remember that you can draw your
diagram in a very large circle to begin with and then scale it down
to size later.)
Artwork: How a plasma TV works. Here I'm using a pullout (the grey circle on the right) to show what happens inside one pixel of a plasma TV screen (the colored grid on the top left). It could be more obvious that this is a pullout. Maybe I need to make the pullout lines darker or fade the colored grid into the background a bit more? I shouldn't have to explain to readers that this is a pullout: that should be obvious from my drawing—and I think I do have a bit more work to do here.
Find out more
If you're interested in using visuals to communicate, you might find these pages interesting:
- Edward Tufte: The guru of technical, visual communication. His books are legendary examples of how to turn often incredibly mundane information into beautiful artworks that communicate clearly.
- David McCandless: Working in the same broad field as Tufte, but more colorfully and perhaps with a little more "surprise and delight."
- Flickr: Data visualization: A Flickr pool that curates interesting charts, infographics, and other kinds of data visualization.