The difficulties of the aerial survey of the Aletsch Glacier lay in establishing ground control in the high mountains and locally on the moving glacier surface, and in plotting featureless névés on the autograph. The major problem in plotting proved to be the delineation of the margins of active glaciers where marginal zones were thickly covered with debris or fresh snow, or where it was necessary to define the boundary between the active glacier and stagnant ice. The distinction between active and stagnant ice is based on movement and nourishment, that is, on characteristics not directly visible in the air photographs, and the boundary is too often a matter of personal judgment. The authors hold that this boundary would be better omitted on an accurate map of the type discussed, while the glacierized area should be represented only in so far as ice is clearly indicated by surface features. A further provisional boundary might be given to indicate suspected buried ice. The paper emphasizes the importance of favorable glacier conditions when the control photographs are taken, to facilitate the mapping and interpretation of glaciological features.