Affordances, Constraints, and Mapping

The world of design owes Donald A. Norman a tremendous debt for his application of principles of psychology and cognitive science to the understanding of our interaction with the designed world. It is not a novel view to praise his The Psychology of Everyday Things, that evolved into The Design of Everyday Things and which set out ways to understand the nature of our interactions with design. He later balanced this "functional" view with Emotional Design: Why we love (or hate) everyday things. Together these books enable the reader to understand the underlying, but often hidden, patterns that are supporting what we're doing or, more often, obstructing it. I've found the following three  of Norman's principles particularly useful to help design students as they come to understand the nature of design experience:

Affordances,

Contraints, and

Natural Mapping.

I can't add to Norman's brilliant articulation of these principles, nor to their further distillation in the book Universal Principles of Design, but I can illustrate examples of them, and address some of the confusion students have found in understanding the application of these issues to design over the years.


Affordances

There are two types of affordance: cognitive and physical. A good cognitive affordance is something that directly and intuitively reveals a design's use or purpose and a good physical affordance is something that directly and intuitively shows how it can be used. Both were present in the handle for the original iMac. Jony Ive, the computer's chief designers, explained the design rationale, saying: "Take the [original] iMac, our attempts to make it less exclusive and more accessible occurred at a number of different levels. A detail example is the handle. While its primary function is obviously associated with making the product easy to move, a compelling part of its function is the immediate connection it makes with the user by unambiguously referencing the hand. That reference represents, at some level, an understanding beyond the iMac's core function. Seeing an object with a handle, you instantly understand aspects of its physical nature -- I can touch it, move it, it's not too precious." (Jonathan Ive).

A bad affordance is something that cognitively and/or physically fails to "afford," to support a desired action or activity. In the example below there is the tell-tale sign of a design failure, a post-hoc "unofficial" label indicating that the affordance to "push" was unclear, most likely with the result of the gray handle being pulled off, thus prompting the intervention (found on all dispensers throughout this building, but not others on campus featuring the same product).

 

In the picture above the handles say "push" and this has, post-hoc, had to be addressed by letters saying "pull." But, still, the immediate an overriding message of the door to the patron is "push," therefore the choice of this hardware results in a bad affordance. The way this works can, perhaps, be better seen in the following example:

Here, to an even greater degree, the "push bar" says, naturally, to the user "push." Again, and based on repeated issues, stick on letters saying "pull" have been added. But, as this picture shows, that message is cognitively drowned out by that of the push bar, which is hierarchically more important. We know this from observing the wear on the word "Pull," which have been worn down by people -- pushing! This is all remincent of the Far Side cartoon that I hope I don't get sued for including. It speaks for itself:

As noted above, and as Don Norman clearly points out in The Design of Everyday Things, if you want to identify problematic designs look for those where a little sign has been made after the fact. This indicates that the design isn't working as intended of, if there was no intention, isn't supporting the activities that are actually taking place -- this to the point where someone working in the area has been motivated to try to arrest the aggregate, and inappropriate behavior, with a sign or post it note. This is the case in my local municipal building in Brown County, Indiana:

Here post-it notes have been used to correct two (and a half) design flaws. The first, on the left, the "misreading" of the window on the right as a door and, second, the lack of an affordance on the actual door to indicate whether to push or pull, and whether the door swings from the right or left.


Constraints

Sometimes students get confused and think a constraint is a bad affordance -- not true. A good constraint signals and prevents an action that is undesired and a bad one fails to do so. According to Lidell, et al, as with affordances, there are two types of constraint: 1) cognitive and 2) physical, though both can be present in one design situation.

In the case above brass "knobs" have been inserted into the limestone to physically constrain -- to prevent -- skateboarders from sliding their boards along the edge and thus scarring the stone. This is a reflection of pro-active design intent. In the case below, from the Renzo Piano Building Workshop's design for the Modern Wing at the Art Institute of Chicago, what appears that a post-hoc constraint has been added to prevent people from absent-mindedly walking into the back of the stairs (open, as they are, in conformance with the concept of transparency that guides the design:

Though I like the design, and Piano's work overall, this constraint could still pose a hazard. While it might prevent one from banging into the steps with one's head, it could still "afford" falling, for those not paying attention.

Constraints are omnipresent in product design. In the following case, that of a European shower control, the black nub sticking up must be pushed and released in order to turn the handle so that water above a certain temperature -- it constrains getting burned unwittingly. (Though I have known people to take lukewarm showers while in Europe or on some cruise ships before understanding the nature of the constraint).

Another example can be found with the evolution of "thumb," (anthropomorphism there) or "flash" drives. These have become smaller and smaller and the designs for them more innovative, or at least outlandish, over time. In addition to the risk of losing a memory stick with important files, I have one which is a case of reductio ad absurdum. USB drives are "sided," i.e. it only goes in one way, as is the Apple 30 pin plug, latterly used for the iPod, iPhone, and iPad. For this reason most traditional flash drives have an outer sleeve that serves as a constraint, prohibiting one from inserting it in the wrong way, something that is not particularly harmful, but that will not work because an electronic connection will not be made. As one can see in the two pictures below, the connector is not centered within the constraining sleeve.

The actual connection is made between the cable end and the lower side of the projection within the opening below:

In the photo below, the drive on the right has a built in constraint to ensure that it can only be inserted in the correct orientation, The PNY drive to the left is "cool" but, lacking the constraint, it can be inserted in either direction and it it only when the drive doesn't show up on one's desktop that the failure to connect is recognized. (Additionally, it is very easy to to extend the drive fully out of its sleeve and so fail to make a connection, even when in the correct orientation).

One of the implicit questions of Don Norman's The Design of Everyday Things seems to be, "don't designers think things through, or at least try them out?" Part of the problem may be that since designers know how the things they work on are supposed to work that they don't encounter the same issues. This is way valid user-testing is so critical to design success.

Sometimes we can learn the most from the improvisations made by those who have no design training, and no knowledge of the principles at all. While waiting to see my allergist one day, and trying to ignore the room's decor, I found the following improvised constraint:

It is a bit difficult to see, but the broken tennis ball was added to the back of the chair to keep the metal piece on the back from scarring the wall.

Other examples of constraints would be the chair rails on walls to prevent damage, and "rope lines" in banks, the airport, or at Disney World, to guide -- constrain -- users' path to their destination.


Natural Mapping

Mapping, or natural mapping, is concerned with the relationship of a mental model we have in our head to items we encounter in the world. In the case below, of a lock on a bathroom door at a bank which, incidentally, opens directly onto the lobby, one's intuition -- one's mental model -- might be that the movable piece on the lock would go towards the door, indicating locking. Instead the design is counter-intuitive and so, the tell-tale sign of bad design, a hand-produced sign has been added in an attempt to compensate for the bad initial design.

Mapping relationships can be found everywhere. Below, for a similar task -- locking and unlocking a car -- the same parent company, Volkswagen, have approached the task in different ways. On the left my Audi A4 has switchgear in which "lock" is up and unlock is down, whereas for my wife's VW Tiguan in the middle it is the opposite (apologies for the poor picture quality). "Down" for lock and "up" for unlike may go back to the days of manual door locking and so maybe it's a cultural precedent that has little relevance today.

The electronic seat controls on the Audi, however, provide an excellent example of natural mapping:

Looking at the side of the drivers seat starting from right to left we find a vertical control, roughly in the shape of the seat back, with can be used to move the seat back -- the mental model for forward and back can be mimicked through moving the handle forward and back, which controls the seat itself. It's a good mental model because the way we intuitively think it should work is the way it actually works. Similarly the middle control, which resembles the shape of the seat itself, can be moved forward and back and up and down -- all without looking at it -- and achieve the desired, i.e. the expected, result. From this angle the right and middle controls map the relationship to the seat itself. The control on the left is a bit less intuitive but controls the bolstering and support withing the seat and the back.


More Doors

As we've already seen, despite their simplicity, doors often possess problematic affordances, inadequate constraints, and counter-intuitive mapping. Here's a few:

The image above, from a terminal in Costa Rica, would have been better had the door been completely closed. One can imagine the sign resulting from people trying to "push" their way in, as was the case with the gifted child in the Far Side cartoon presented earlier

The door in the image above correctly says "push," with it's bar, but the bar does not have an affordance indicating which side to push on, so a sign has had to be added to tell the user what to do. Interestingly, the sign is placed at eye level which reflects that the initial action of pushing is instinctive, whereas the sign is an attempt to cognitively override that action. (This is something that could be easily studied using action research, logging the amount of time -- they delay -- that this one lack of design attention -- caused users).

Above is the door to a men's toilet (using their terms) in the Imperial War Museum North in Manchester, England, designed by Daniel Libeskind. The symbol of the man is quite visible, having high contrast and large size, but the handle says "pull" The red circle, in keeping with the design language of the building as a whole, says "push," again at eye level reflecting the users must take a conscious action to compensate for the inherent frustration embedded in the design of the door itself, and the hardware specified.

Above is the main entrance to Libeskind's building. In this case the affordances are quite clear, the handles suggest "pull," but a sign saying this has been added to the door on the right. The universal design principle of "equitable use" is also present in the choice of windows which allows people who are tall or short (or chair-bound) to see through the door.

This gasoline pump in Nashville, Indiana, is one of the most ill-conceived designs I've ever interacted with. The various written notices -- official and post-hoc -- are clear indications that many aspects of its method of use are perceived to be unclear. First, the manufacturer has added a sign to indicate the required orientation of the credit card. Next, a post-it has been added to inform the user to follow the instructions on the screen. Third, an improvised green "start" spot has been placed over the original design to make it more hierarchically important. Why it should be necessary to press a start button, rather than just initiate fueling by pulling on the pump handle, as is often the case, is an outstanding question. Oh, and the fuel flows extremely slowly and the machine "beeps," signaling nothing, it seems, through the fueling process.


Conclusion

In my work with students over the years I've found these three ways of looking at design, and our interaction with it, are extremely beneficial. These principles are particularly important for product, software, and interior designers who are charged with creating the interfaces -- cognitive and physical -- between people and design. With principles as clear as this there is no reason to ever get it wrong! Thank you Don Norman! Clearly there is much more to his work that I have presented here, but these practical applications are a great way to begin to explore these topics.

Note

Signifiers

According to Norman, from the feedback he received over the years, "affordances," was found by many to be be a confusing concept. Norman, in the revised and expanded edition of The Design of Everyday Things, discusses the origins of the term "affordance" in the world of psychology and his application of it to that of design. He then introduces the reasons why he thinks the word "signifier," from the field of semiotics, is a more appropriate choice of term. He says: "Signifiers can be deliberate and intentional, such as the sign 'push' on a door, but they may also be accidental and unintentional, such as our use of the visible trail made by previous people walking through a field or over a snow-covered terrain to determine the best path. Or how we might use the presence or absence of people waiting at a train station to determine whether we have missed the train." In my own case, I need to spend some more time contemplating Norman's intention behind this change of terminology. On first reading, however, it seems he is going into more detail on the nature of the relationships between objects and our cognitive interactions with them.

References

Jonathan Ive /Winner of the Design Museum's Inaugural Designer of the Year Award in 2003. Retrieved on February 4, 2014 from http://designmuseum.org/design/jonathan-ive

Lidwell, W., Holden, K., & Butler, J. (2010). Universal principles of design: 125 ways to enhance usability, influence perception, increase appeal, make better design decisions, and teach through design. Rev. and updated. Beverly, Mass.: Rockport Publishers.

Norman, D. A. (1988). The psychology of everyday things. New York: Basic Books.

Norman, D. A. (2002). The design of everyday things. 1st Basic paperback ed. New York: Basic Books.

Norman, D.A. (2013) The design of everyday things: revised and expanded edition. New York: Basic Books.

Norman, D. A. (2005). Emotional design : why we love (or hate) everyday things. New York: Basic Books.


Image sources

All photographs by the author, except:

imac G3. Retrieved on August 29, 2013 from http://www.maclife.com/article/feature/complete_imac_history_bondi_aluminum

USB cable. Retrieved on February 4, 2014 from http://i.i.cbsi.com/cnwk.1d/i/tim/2012/01/20/USB_cable_generic_610x458.jpg  

USB port. Retrieved on February 3, 2014 from http://simple.wikipedia.org/wiki/Universal_Serial_Bus

Car door lock. Retrieved on February 3, 2014 from http://www.airadvice.com/pr_article/disappearing-monitors/