real world columns: people flow

The ringing of church bells in England has a long history, almost 4,000 years of it. Much of it is tied up with religion, community and church architecture. However, there are small fragments of it that have something to do with interaction design.

The particular example I am thinking about is the tower in St. Mary’s church in Launton, Oxfordshire, England. Here, it was the custom of the bell-ringers to take a barrel of ale into the tower with them to fortify them through the prolonged bouts of ringing in cold and damp conditions. Naturally enough, the vicar took a dim view of these proceedings and when the time came to make some alterations to the church he added a few of his own. As a result the bell-ringing room of the tower was moved up to one floor above ground level, as was the doorway which was reached by an outside ladder. Furthermore the doorway itself was built to be extremely narrow, just wide enough for a bell-ringer to squeeze through and certainly not wide enough for anyone to get a barrel of ale through.

Controlling the passage of people and things through entrances is a key part of the design of built environments, (with parallels in the digital world). The goals of such control are usually restraining traffic to be in one direction or only allowing a particular segment of the traffic through.

A good example of the former is the classic piece of beekeeping technology; the ‘Porter bee escape’ in effect a one-way valve for honey-bees made of two thin prongs of metal pressing gently against each other, bees can squeeze through in one direction but they can’t get back. Isolate a part of a beehive with such a thing and two weeks later all the bees have found their way out and the honey combs can be removed completely bee-free. In the ‘people world’ such one-way valves take the form of turnstiles to allow people to leave a paying attraction like a museum or gallery without allowing unscrupulous customers to sneak in the back-way without paying.

The other goal, that of allowing a particular segment of the traffic through, goes back all the way to the countryside where there is a great variety of mobile animal life, all of which has to be controlled in some way. The old English ‘kissing gates’ (no idea where the name comes from) are simple gates that can’t be left open accidentally for cattle. Wider gateways make use of cattle grids, these are open grids on the ground whose gaps stop cattle walking over them but allow people and cars to go over. Unfortunately the cattle grid filtering also catches other small-footed creatures such as very young children and hedgehogs. Newer cattle grids have small ramps built in to allow distressed hedgehogs to return to ground level. There are many other examples of this ‘filtering’ of users. On a domestic scale there are electronic cat-flaps coupled with special cat collars to enable the flap to distinguish between your own little bundle of furs and purrs and whatever those mysterious other things are that squeeze through at night and trash the kitchen. An even smaller example are the ‘childproof’ tops on pill bottles. The top can only be removed by means of a complex combination of pressing, turning and lining up of arrows. Once again the filtering is not perfect and older people (who are the ones most likely to make use of medicine) often have to enlist the help of twelve year old grandchildren to get the tops off. Road traffic has equivalents with things like speed bumps (which in England have the improbable name of ‘sleeping policemen’) these punish fast moving cars without harming slow moving cars. I imagine that hedgehogs have little problem with them but one side effect is that they also discriminate against cyclists moving at any speed. The general rule with any of these filtering approaches is to identify the target group you want to stop / slow down and then base the design on features of that target group that are not features of any other group or sub-group.

On the web there are peculiar parallels to the whole science of controlling people flow. If you have a fill-in inquiry form for prospective customers you may want to make sure that it isn’t used by students. In e-commerce systems you may want to allow people with an American postal address into the ordering area but divert the others to another area in case they discover interesting discrepancies in the company’s global pricing strategy. How can you tell them apart without interrupting their shopping spree with boring fill-in forms? There is a danger that the resulting user experience can end up like suddenly having to fill in a tax return in the middle of Macy’s department store.

Such filtering of users is also at the heart of some interactive games, where progress from one level to the next is only made by accepting some extremely difficult challenge. Remember the door from the monastery in the TV series ‘Kung-Fu’? The only people who could leave were those that could pick up a red-hot bucket of coals with their bare forearms. No idea how the hedgehogs would cope with that!