The semantics of spatial relations have been intensively studied in linguistics, psychology, and cognitive neuroscience. Angle, distance, and shape are widely considered to be the key factors when establishing spatial relations. In this work an empirical study shows that previous theories overemphasize variation and we clarify the interdependencies between angle, distance, and shape with respect to the acceptability of projective relations. It turned out that the angular deviation plays the key role for relations of this class. The degree of deviation was dependent upon the extension of the reference object perpendicular to the canonical direction of the relation. There was no major effect due to the distance. However, distance interacted with the angular deviation if the located object was very close to the reference object. The experimental results can now be used as a theoretical framework for validating existing computational models of projective relations for their cognitive plausibility