These bitmaps will only show in GNE version 6.0.3 or higher. The Width Status dialog box has the ability to display all the available bitmaps by number. Bitmaps do not seem to slow GNE's various operations by any significant degree, but metafiles and plot files from networks can become quite big if there are many nodes with large bitmaps. GNE's labeling procedures were not modified to handle bitmaps, so node labels may not appear in convenient locations relative to the bitmap. Some experimentation with each bitmap may be necessary to achieve good label placement.
Bitmaps have several interesting uses beyond making the network look less boring.
For example, it is possible to create a suite of several similar bitmaps of varying sizes. Then node size expressions can be used to select a bitmap of a specific size from this suite. Furthermore, it is possible to create a node type for simply displaying bitmaps at random locations on the network. Thus, it would be possible to decorate the network with road signs, signal heads, points of interest, logos, direction arrows, etc. Because this is an experimental feature, we would like to hear back from users about their experiences.