Integrating spatial information is a crucial step in construction of Urban Planning Domain Ontology (UPDO), and taking spatial information from the web as the input of self-learning method are commonly used in constructing ontology. In this case, the use of place names could be important indicators of understanding the spatial information on the web. However, place names expressed in natural language bring diverse ambiguities, which would bring great challenges to several research fields such as Geographic Information System (GIS) and Geographic Information Retrieval (GIR). GIR has more contribution on place name ambiguities than GIS. Nevertheless, from the perspective of the urban planning domain, it is still lacking in application. This paper is a position paper that aims to bring out an argument of place name ambiguities in UPDO, and introduce two kinds of ambiguity frequently appearing in the urban planning domain. The paper also proposes a hierarchical structure of spatial ontology that allows constructors to deal with ambiguities. We believe in that the ambiguity issue is critical for urban planning, and the argument is worth discussing to all relevant domains.