"Many cities face the challenge of making new construction compatible with the character of preexisting neighborhoods. This issue is called contextual urban design. Nearly all US cities have regulations regarding contextual design. European cities such as Berlin, Dresden, and other cities undergoing economic expansion due to German reunification or the spread of free_market economies into Eastern Europe can also expect to face similar challenges. However, traditional urban design notions such as 'context", "compatible", and "neighborhood character" are so indefinite that they create confusion rather than provide the information required for making planning decisions. One solution is to recast those principles from their indefinite forms ("Buildings should be consistent with established neighborhood character" ) to definite concepts based on configurations of material in three dimensional space. The indefinite concept of neighborhood character" can be made definite by expressing it in terms of frequencies of design features within a specified geographical area. For example, in a block of nine houses, the feature might be the number of stories. If all nine houses were one story, the character of the block would be "one story". If all nine houses were two story, the character of the block would be "two story". But what of the intermediate frequencies: I one story in 8 two stories, 2 one story and 7 two stories, etc.'? How many deviations can there be before the overall impression breaks down? This paper reports experimental evidence on the relationship between the frequencies of design features and the percentage of respondents who attribute a design feature to the overall character of the block. Three design features were tested: building heights (two and three stories), architectural styles (Craftsman and Spanish), and roof silhouettes (flat and hip). Altogether twenty-four blocks were tested. The results will provide urban designers with preliminary estimates on how fragile (or perhaps how robust) overall impressions of visual character are. They will also provide a method researchers can use to conduct future studies on relationships between definite physical design features and indefinite overall impressions."