Nowadays, “Smart City” is a very growing and promoting concept. Unlike other concepts related to cities, like digital or green city, it encompasses all technological, human and institutional factors. However, there are too many different viewpoints and definitions of this concept in the literature. The problem statement of this research is that despite the existence of many points of view and definitions for the “smart city” concept, the management part of a particular city needs to formulate a special definition of “smartness” based on the specific characteristics, goals, priorities, policies, and constraints of that city. This paper provides urban planners and managers with an approach that helps them to determine a set of validated, customized and prioritized characteristics for the target city. These characteristics can be used to formulate a desired definition for the city, as an input for strategic planning of a smart city, a guide for aligning the main goals of a city, and a criterion for prioritizing the urban projects for a particular city. Our proposed approach consists of two phases. The first phase is based on a thorough content analysis on the significant body of the literature in order to take a valid and acceptable range of different viewpoints and characteristics of the smart city notion. The second phase relies on the characteristics resulted in the first phase and involves a specific form of validation, customization and prioritization steps for a particular city so as to determine a set of unique characteristics based on the upstream documents and stakeholders’ opinions. In order to show the applicability of the proposed approach, we present the results of applying this approach for the city of Tehran, the capital of Iran.