An Investigation of Visual Clutter in the Topographic Base of a Geological Map

Visual clutter on maps is a familiar experience but its precise nature is only poorly understood. Clutter was investigated in an experiment using a 1:50 000 geological map. Twelve representative map reading tasks were used to compare map reading performance on maps which differed only in their topographic base. The aim was to assess the effect of removing topographic symbols which are of only minor importance to the map reader. This reduction in visual clutter significantly improved performance on a number of the questions. Some evidence was obtained to support the hypothesis that line symbols clutter other line symbols, and point symbols clutter other point symbols, but there is little effect between the two. In practical terms the removal of minor point symbols and type led to larger improvements than the removal of minor line symbols, even though more of the latter were deleted. The relevance of the experiment to other geological maps, and to maps in general, is discussed.