## 4 Literature Review
### Guidelines and Usability Heuristics  
In the 1990s, [PERSON] proposed a series of usability heuristics to evaluate user experience in digital interfaces [22]. These heuristics are probably the most well-known and most widely applied when it comes to evaluating user experience. In addition to [PERSON], other works have presented proposals for evaluating the usability of interfaces. [PERSON] [23] offers 21 interaction principles that should be observed for any interface. [PERSON] [24] developed 9 cognitive principles to improve a person's performance when using a computer. [PERSON] [25] formulated 30 principles for designing usable interactive systems that are grouped under seven broad sets. Within the reviewed literature there are also principles and guidelines that have a more specialized focus or perspective. There are also those that center on a particular plane of the user experience. The psychological heuristics offered by [PERSON] [26], or the principles of [PERSON] [27], consider performing evaluation from the perspective of a user's senses and reasoning when using an interface. The Web Accessibility Initiative, which calls on version 2.0 of the Web Content Accessibility Guidelines (WCAG 2.0) [28], establishes rules for creating web content that is more accessible for people living with some form of temporary or permanent impairment (visual, auditory, motor, speech, language, learning, neurological or cognitive function). They also consider certain steps to improve content for elderly people. The Biomechanical Institute of Valencia [29] has developed a list of 12 parameters to check how well ATMs perform in terms of accessibility. Regarding the internationalization and adaptation of interfaces to people from different cultures, [PERSON] and [PERSON] propose 7 elements for designing an interface aimed at international users [30]. A summary of the literature review is presented in Table 1 together with some additional characteristics. The table also includes a description of the limitations that would make these reviewed proposals unsuitable for use with urban interfaces. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Author**} & **Number of Guidelines,** & \multirow{2}{*}{**Main Objective**} & **Limitations in the Context** \\  & **Principles or Heuristics** & & **of Urban Interfaces** \\ \hline \multirow{2}{*}{[PERSON] [22]} & \multirow{2}{*}{10} & Provide criteria for & Does not consider evaluating \\  & & designing and evaluating & the physical setting in which \\  & & interface design. & the interface will operate. \\ \hline \multirow{2}{*}{[PERSON] [23]} & \multirow{2}{*}{21} & Evaluate user interactions & Focuses primarily on the \\  & & with the interface. & design aspect of the \\ \hline \multirow{2}{*}{[PERSON] [24]} & \multirow{2}{*}{9} & Improve the performance & Mainly steered towards the \\  & & and efficiency of a person & efficiency of executed tasks. \\ \hline \multirow{2}{*}{[PERSON] [25]} & \multirow{2}{*}{30} & Provide principles for & Focuses on digital aspects, \\  & & interactive system design. & does not take setting or \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of Revised Usability Heuristics and Guidelines. Although all these heuristics, guidelines and principles are useful for designing user-centered interfaces, they are not tailored to many of the situations affecting an urban interface, as detailed in the objectives and hypothesis of this article. Authors such as [PERSON] [33], [PERSON] [20] and, more recently, [PERSON] [19] have explained that the use of heuristics and guidelines specifically tailored to certain contexts helps to evaluate interfaces that have a set of unique characteristics, as in the case of urban interfaces. This being said, the literature review has revealed that the referenced authors fail to contemplate certain angles that must be considered in the case of urban interfaces.