Some people get very confused with right and left when driving (“Turn left here. No, the other left!”) I knew a girl who wrote “left” and “right” on the ends of her windshield with a sharpie, and it worked well for her.
Another solution is to use concrete terms, instead of abstract terms:
“Turn left” is “Driver-side turn”
“Turn right” is “Passenger-side turn”
Sailors have been using the concrete terms “port” and “starboard” for centuries, for the same reasons.
Displays are getting sharper all the time. Sharpness is very important, because things don’t just look better on high-resolution displays; they are measurably faster to use.
Low-resolution monitors (including all computer screens until now) have poor readability: people read about 25% slower from computer screens than from printed paper. Experimental 300 (PPI) displays (costing $30,000 (in 1998)) have been measured to have the same reading speed as print, so we will get better screens in the future.
The resolution of a display is measured in PPI, Pixels Per Inch, the number of pixels used to draw a one inch long, one pixel thick, line. A higher PPI means smaller pixels, and clearer images. You can calculate the PPI of your screen by
PPI ≅ sqrt(pixels_across^2 + pixels_down^2) / diagonal_inches
I am writing this article on an iMac with a 24″ screen, showing 1920 x 1200 pixels, so my PPI ≅ sqrt(1920*1920+1200*1200)/24 ≅ 93 PPI.
The resolution of a printer is measured in DPI, or Dots Per Inch. Unfortunately, DPI is often used as another term for PPI. That is technically inaccurate, but even Microsoft does it. SPI, Scans Per Inch, is another term that is used instead of PPI, but fortunately is correct when describing digital displays.
Bitmapped images are smaller on high-resolution displays, because the pixels the picture is made of are smaller. This can be a big problem for interface elements.
For example, today Apple’s interface guidelines say “The standard Help button is 20 pixels in diameter and should be placed at least 12 pixels from other interface elements.” On my iMac, a 20-pixel wide circle is about 0.21″ in diameter — roughly 1/3rd the diameter of a Dime. 
But on a 300 PPI display, it would be 0.07″ in diameter — roughly as thick as three pieces of mechanical pencil lead 
. As you can see, it’s way too small to comfortably click!
Just scaling bitmapped images, so a 20-pixel wide picture is always drawn 0.21″ wide, isn’t a good work around. It’s just emulating a low-definition, low-readability, display on a more expensive high-definition display. Another problem is that it looks terrible when everything else on the system is crystal clear.
It gets more ugly when the scaling-factor is higher, say for a display that matched the print fidelity of the tawdry magazines you see in the grocery check-out isle.
A resolution independent interface can be usably, and pleasantly, displayed on high-definition or standard-definition screens. There are two ways to build a resolution-independent display.
You can use vector images, which can be resized without problems. SVG and PDF are two popular formats. This sounds like an elegant “design once, show anywhere” solution. But in practice today building a vector image of the same quality as a bitmapped image can be very difficult, especially with complex images. This will change in time. Today designers create bitmap images by embellishing a vector image with bitmap-effects. As vector-imiging tools improve, they will be able to perform equivalent effects, but in a resolution-independent way.
Alternately, your app can carry-around a set of bitmapped images and draw the one that most-closly matches the current resolution. If you only have to support a handful of well-definied resolutions, this might be the best choice with today’s tools. The only caveat is that all signs point to vector-images being the future. Loading one vector image is also easier the selecting one of many bitmapped images to load. (And theoretically a vector image won’t have to be tweaked if we suddenly get one million PPI displays).
Already Solved
I think it’s important to note that Fonts have been facing an even more severe resolution-independence problem for decades, and have mostly solved it. The same font can be rendered well on a 1200 DPI printer, and a 72 PPI display. That’s a much bigger resolution disparity then a computer interface will ever have to deal with, because by the time a screen close to the resolution of a 1200 DPI printer is common, nobody will be using 72 PPI displays anymore (they aren’t even sold today).
Early fonts were bitmap fonts — a collection of bitmaps of what the font should look like at a particular scaling. But today vector fonts have replaced bitmapped fonts on the desktop, and even the iPhone. Vector fonts let us do amazing things with scaling (font specific stuff starts at 1:18). Vector fonts have been such an unqualified success, that it’s hard to imagine vector images not replacing bitmapped images for interface elements.
When Will It Happen
Year
Model
ResolutionSize DPI 1984
Original Macintosh512 x 342 9″ (8.5″) 72 1984 640 x 350 13″ (12.3″) 60 1994
Apple Multiple Scan 17 Display1024 x 768 17″ (16.1″) 80 2004 Apple Cinema HD display
2560 x 1600 30″ 100 I used the Tag studios Monitor DPI calculator to arrive at the DPI numbers in the above table. I couldn’t quite figure out what the actual displayable area of those early CRT monitors were, so I estimated about 5% non-displayable area based on the diagonal measurement.
Regardless, it’s sobering to consider that the resolution of computer displays has increased by less than a factor of two over the last twenty years. Sure, displays have gotten larger– much larger– but actual display resolution in terms of pixels per inch has only gone up by a factor of about 1.6.
I can’t think of any other piece of computer hardware that has improved so little since 1984.
It certainly doesn’t not look like we will get 300 PPI displays anytime soon! At the present rate, it will be decades before a $2000 display matches the clarity of a $20 printer.
However today’s smarphones and small-devices have much sharper screens then computers. The first generation iPhone is 160 PPI, the Kindle
UPDATE 2009-02-11: Wikipedia’s list of devices by PPI lists some very high PPI devices. The Sony Ericsson X1
phone has broken the 300 PPI “readability threshold”. The Fujitsu Lifebook U820 has a 270 PPI display. But the screen is only slightly bigger then the Osborne 1 “portable” computer of 1981. Still, if history is any indicator, once better technology is actually sold, it catches on very quickly.
time = a + b*log2(distance/target_size + 1)
This is far and away the best article on Fitts’ Law I’ve seen.
The Accot-Zhai “Steering Law”, which predicts how quickly a person can “steer” something down a 2-dimensional road without “crashing” can be derived from Fitt’s Law. As you would expect, the wider the road, the faster it can be traveled. This might be my favorite implication of Fitt’s Law, since it implies that my small car may have a higher “usable speed” then a bulkier muscle car. :-p
…a study done at Apple almost ten years ago found that the user’s mouse gravitates toward red objects almost as though they were possessed with magnetism. The study forced us to abandon the idea of making close boxes and the Shut Down option red.
I am interested to know if this is still true when you are using your own finger to directly touch a red screen element. I expect it still is true, but you never know for sure until you test. Real fingers don’t tend to be drawn towards real flame, even if cursors are drawn to animations of flame.
Here is a handful of lesser-known Mac OS X keyboard shortcuts that I’ve found to be very useful for working with text. They work in all standard text-fields, which means they work in most programs. Sadly, they don’t work in Microsoft products, and a few other apps that use non-standard text fields.
option = you will see the mouse cursor into a + , and you can now select columns of text! Unfortunately it only seems to work in editable text-fields, which is a great shame.
ctrl + d = forward delete, even if you don’t have it on your MacBook’s keyboard.
ctrl + a = Go to the beginning of the line the insertion-point is on.
ctrl + e = Go to the beginning end of the line line the insertion-point is on.
ctrl + k = “kill the current line”, deletes everything from the right of the insertion point to the next newline. This is very useful in Terminal, because you can delete the tail of a long command
command + delete = “Delete To Beginning Of Line”. Just like ctrl+k, but backwards, not forwards. (It even puts the killed text on the yank-pasteboard — don’t worry if that makes no sense, it’s an emacs-ism I don’t find useful.)
And yes, that’s ctrl, not command, because these are shortcuts inherited from the old UNIX text-editor emacs. There are more emacs “key bindings” that are available, but I have never found them useful. This long list of Mac OS X keyboard shortcuts includes them.
command + ctrl + d = look up the word under the mouse in the dictionary. I can’t believe that other operating systems haven’t done this for decades, it’s that useful.
It is unfortunate when programs use text-fields that do not support commands the operating system should give to every application. It’s always a mistake. Fundamentally, not supporting ctrl+a (go to beginning) is no different then not supporting command+c (copy).
If you find these commands useful, please teach them, and let developers know it’s a problem when you can’t use them. That will improve computing for everyone.
I hadn’t realized until today that “zooming” was a nontrivial task. I’m habituated to choose “zoom in” to see more detail, but less of the big picture, and “zoom out” to see how less-defined blocks fit together. But selecting which flavor of zoom is appropriate is not as easy as it first appears.
I didn’t realize this until I saw two participants in usability tests frequently choose the opposite kind of zoom from what they wanted. One lady would even explain how zooming would be helpful to what she was going to do, then say that she should perform the opposite kind of zooming that she described.
Understanding zooming involves forming and manipulating a three-dimensional model of abstract data represented on a two-dimensional screen. Sometimes there’s even the question of what is being zoomed. If you zoom in on a window containing a map, should the window itself change size (take up the fullscreen perhaps), or should the contents of the window be changed?
Small wonder then that some people choose the wrong kind of zoom, especially if they are not spatially-oriented.
The good news is that a zoom error is easy to recover from. You just hit the other button. Recovery is even easier if a knob, or other reversible input device, controls zoom. You just twist in the opposite direction, without having to acquire another button first. The scroll-wheel on a mouse is such a control, but …
But be careful when using the scroll-wheel to zoom, because users may trigger a zoom when they meant to scroll. I have this problem all the time with Google Maps. After a few hours of using the scroll-wheel to scroll webpages, I look something up in the Google Maps webpage — but if I attempt to use the scroll wheel to scroll the map it shoots my viewpoint up hundreds of miles into the atmosphere. Even though recovery is easy, it’s very disorienting, and quite annoying. It’s also slow, because the data has to be loaded over an internet connection — even the fast connection at the office is still orders of magnitude slower then loading the data from local memory.
It’s interesting that Mac OS X’s Exposé feature, while arguably a zooming-interface, is not described as one. To quote the help, “Your computer includes Exposé, a tool that temporarily rearranges windows to help find things.” No spatial reasoning is needed to use it.
Most diction decisions, like choosing the keyword nil over NULL seem inconsequential. Sure, n-i-l is probably faster to type then shift+n-u-l-l, but the difference is too small to matter. Both terms are clear.
However after today I’m convinced that the C++ convention of using the keyword this, over self, was a mistake. “This” is just too common of a pronoun. It’s too easy to say something like “..this is invalid..”, and leave people wondering if you meant that-this or self-this.
I’d be interested to know the reasoning behind choosing the ambiguous keyword “this” over the precedent “self”.
I plan to refer to “this” as “self” whenever possible for a time, to see if it’s less confusing, even to habitual C++ users.
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