In the paper, the main concepts about a design tool supported by an object database system will be described. The design tool should improve architectural design with respect to analysis and improving existing and planned urban environments regarding several quality criteria, especially those associated with visual aspects. Preconditions for defining the design tool's purpose are the determination of the "well-situated" urban elements, their impact on cognitive mapping, and the exploitation of thisknowledge on cognitive mapping for the improvement of urban environments. Cognitive mapping is a kind of representation of schematic knowledge that a person has about familiar environments. A cognitive map is stored information or knowledge about the purpose and function of the environment. This leads to the conclusion that an urban environment design which takes of the process of cognitive mapping into consideration, will be experienced by most of the people in the same way. Investigationsof this process result in a theoretical model of elements of urban environments, their relationships and their dependencies. The theoretical platform of the tool is based on design theory, cognitive science and computer science. Design theory and cognitive science will be used to develop the theoretical model. This theoretical model together with computer science will be the basis for tool development. The tooluses a schematic representation of urban environment, based partly on Lynch's theory of "urban form". Lynch's theory is crucial for the tool because it explains almost all elements of urban environments. Systematic investigation of urban environments and their characteristics are important for theoretical modelling as well as for the later computational modelling of the tool. The main computational support for the tool will be provided by an object database system, which helps to represent and to handle all the urban elements with their properties and relationships, with their natural semantics. The information represented in the database will be used to analyze urban environments as well as to improve and control their visual quality.