The Smart City is a possible evolution of each City. With the rapid development of information technologies applied everywhere in city life, cities are becoming smarter and smarter. However, this context has multiple orientations, supported by an architecture of the assistive system and the associated implementation process. In this chapter, we present several cases of evolution of a city to become smart by integration of appropriate applications and associated assistive services. The integration of initially autonomous applications to a system is natural evolution, conducting to create an assistive system. We begin by the presentation of different smart city applications, then we try to conceptualize this issue and point out the main aspects. We propose also a design methodology with different approaches illustrated by several case studies that attempt to transform a coastal city into a Smart Coastal City. Proposed design methodology approaches and technologies can be used in order to manage the progress of a city to become smarter. We present several cases, supported by appropriate approaches, mainly mobility oriented and indicate their relations with proposed methodology, the role and functionalities of corresponding assistive systems, and the HCIs implemented in practice. Finally, we integrate all these aspects in the architecture of an assistive system managing them.