Demonstration of the dilation operation applied to thesource skeleton identified towards the W51 molecular cloud. The grayscale image shows the dust continuum emission mapped with ATLASGAL while surrounding contours show how the size and shape of thedilated skeleton changes as it is dilated by squares of increasing sizes. The red contour shows a dilation by a square of 1 pixel and simply traces the original skeleton as this also has a width of 1 pixel. The pink, green, blue contours show the structure after the original skeleton has been dilated with a square of width of w = 5, 10 and 25 pixels, respectively.