We describe a method for combining several instances of image feature maps to obtain an 'average' feature map. Applications are shown to radar maps of aircraft flight paths, and line sketches of human faces. The technique is an adaptation of the 'distance average' of random sets introduced by Baddeley and Molchanov. It involves computing the distance transform of each input image, calculating the pixelwise mean (or median or trimmed mean) of distance values, and applying a threshold or ridge-tracing operation to obtain a binary image. (C) 1999 Pattern Recognition Society. Published by Elsevier Science Ltd. All rights reserved.