The term "smart city" has been used in many circumstances, mainly to determine the added value of the "smartness" of a city. The cities must be viable for their citizens, "green", with "empty" spaces, without traffic problems, good infrastructures etc. In addition, a city must be "smart", means providing smart data, smart infrastructures and "smart" applications to their citizens. Many academic papers and real projects have exhaustively analysed and concretised the above issues. Nevertheless, from a practical point of view, there is not a short list of factors extracted from a combination of a) theoretical definitions, b) indexing systems measuring a city’s "smartness" c) the citizens experiential needs and desires for smart applications and d) factors coming from the applications/data provided by local, national and international institutions/governments and private companies. A such integrated list may give a valuable practical level of the "smartness" degree of a city. This article is based on the extraction of the above factors which determine the level of "smartness" of a city. All those factors were applied in the city of Athens in order to determine the level of city’s "smartness".