The goal of this research is to support spatial decision that deals with foreign tourists’ inconveniences in Seoul City—associated with place—by using data mining technology. The analysis of domestic mobile phone records of foreign tourists not only produces the number of floating population demonstrated in the aspect of its nationality and time period, but also conducts the spatiotemporal localization of foreign visitors. R-Studio, a statistical computing software, is used to analyze the spatial density from the call traffic; QGIS, an open-source Geographic Information System(GIS) software, is useful in displaying the data on a map. As a result, fourteen areas, where foreign floating population’s mobility patterns are noticeable, are selected: Gyeongbok Palace, Namsan Hanok Village, Deoksu Palace, Insa-dong, Myeong-dong, Namdaemun Market, Dongdaemun Market, Garosu-gil, Apgujeong-dong, Itaewon, Hongik University, Gangnam Station, COEX, and Lotte World. Further this research introduces the application to alleviate the inconveniences regarding the signposts, bus route, and insufficient tourist information centers; it suggests to add more foreign languages on the signposts at certain locations, modify the current route of the city tour bus, and position additional tourist information centers at the area where floating population of foreign tourists turns out to be dense. Likewise, the connection between big data and GIS technology in this research poses a significant impact on enhancing the efficiency of spatial decision.