## 10 Discussion  
The evaluation of user experience on urban interfaces must not be overlooked and is an essential part of any'smart city'. An evaluation tool that forms part of the design & development cycle or acquisition cycle of an urban interface is of vital importance if user-centered design is to be guaranteed. Using an evaluation tool such as the guidelines proposed in this study will add value if applied to the design and development stage or acquisition stage of urban interfaces. This was not possible in the case of this study as the tool was tested on urban interfaces already in use. Had the eight interfaces been evaluated using the proposed tool prior to their launch some costs associated with poor design could have been avoided, i.e., expenses covering additional support staff to help users use the interface, or additional plugins or hardware to complement the interface functions, amongst others. Although the proposed guidelines were tested in different cities in two different countries, there are more social and cultural contexts in which they should be tested and evaluated. In particular, the tool should be tested on interfaces in rural areas to establish whether people's technical know-how and the infrastructure itself might influence results differently to an urban area [71]. This could lead to the creation of a new guideline or supplements for existing guidelines. Likewise, some communities contain different ethnic groups, thus different customs are practiced within the same community. The internationalization guideline may need to take facets like this into account. The technological trends inherent in a'smart city' [72] that relate to virtual reality, augmented reality or biometric recognition need to be reviewed in order to verify whether they have an impact on any of the guidelines, especially those relating to alternate and complementary digital resources. Figure 32: Interface of Mexico City Government Treasury kiosk. Government staff member needs to help citizens. The amount of data and personal data being collected within a'smart city' is constantly growing [12]. The actions related to the acquisition and use of these data in an urban interface can influence people's perceptions of these interfaces and user experience. Such situations must be evaluated, because a better quality of life for users depends on it and cannot be considered as an isolated element. Interfaces with a user-centered design improve the quality of life as a citizen. For all eight interfaces evaluated, a recurrent issue that was observed was that manufacturers or organizations failed to address accessibility and inclusion. Of the heuristics that were reviewed in the literature, only WAI [28] contemplated the topic of accessibility, and mainly in relation to websites. The remaining heuristics that were reviewed, however, ignore more specific accessibility issues, such as: Accessibility for the elderly; accessibility for individuals living with some form of physical or intellectual impairment, e.g., color vision deficiency; or some form of temporary disability, e.g., a fractured bone. The guidelines proposed in this study do take these issues into consideration. The proposed guidelines raise questions examining internationalization, which in the reviewed literature are only expressly contemplated in the proposal by Russo & Boor [30]. During the field study tourists and individuals who had recently moved to the city were frequently observed struggling to complete tasks. As mentioned previously, when addressing the question of efficiency researchers identify an increase in completion times [53]. For each of the eight interfaces this primarily occurs upon first contact with the interface and when waiting for a transaction receipt or refund from the interface.