The use of 3D-software in architecture has several advantages: architects and clients are better able  to comprehend the design, test variants and take and confirm decisions. On the other hand, architects  warn against the presentation of computer images at too early a stage because these images give the  impression of conclusiveness. Hand-drawn illustrations, by contrast, have the loose character of a  sketch and leave things open to the imagination. This has advantages, especially in the initial stages  of a design. This paper is a survey of our current research and teaching work, showing especially the combination  of freehand drawing and computer model and the effects and possibilities of this form of abstraction in  order to facilitate a correct interpretation of the proposed ideas.