Barrier-free signs, such as a sound device on a traffic signaling mechanism or a Braille on a map,are widely used in a modern society for the benefit of the visually impaired people. This paper proposes a sound-aided tracing system with a mobile touch screen for understanding a structure of an image. The proposed system represents a structural feature of a line-drawing image with a guiding sound. The structural features are extracted from the image and guide sounds corresponding to the features are assigned to the pixels on the image. A prototype of the map guiding system has been implemented. The experimental results with the prototype have shown that the proposed system enables subjects to trace a correct route on the map, although there remain some usability improvements for practical use.