When people get in contact with a new technology it is important for them to quickly get to understand it. They should use it intuitively without having to read manuals or having to contact the support. This way they can get access to the new technology easily and immediate use of the device is possible. Intuitive use is best achieved by using simple, universal layout for the user interface. For example, it is possible to complement buttons or menu items with icons that are either known from other applications or where the meaning can be inferred from the icons' design. The widget for news, for example, can be represented by a newspaper icon. On this Apple Developer Site you can find everything that should be considered when creating a user interface.
Older Users
The development of the modern world is fast-paced. New technologies are spreading fast and are quickly perceived as a standard and then used in devices that are used in public spaces.
But not everyone adapts to the new technology. Especially older users have trouble to get used to new technology at times. Although almost anyone has had contact with a smartphone or a tablet, that does not mean that everyone immediately understands the usage of a ticket machine with touchscreen. Often older users recognize displays as output, but not as input devices. As a result of the widespread use of touchscreens at train stations this is slowly changing. An intuitive user interface is decisive here as well.
A problem, that does not only affect older users, is the problem of impaired vision. For this cases the display should be able to adapt as well (see 'Accessibility').
Buttons vs Touch in a Lift
A large display with a touchscreen in a lift is chic, modern, and enables a multitude of new functions. Realizing the input of calls and commands completely via the touchscreen, however, is not always the best solution. Often complementing options with a combination of touchscreen and tradtional buttons is a good alternative.