Causes and consequences of scale change in schematic maps
ISBN 978-85-88783-11-9
Authors
1Forrest, D.
1UNIVERSITY OF GLASGOW Email: david.forrest@glasgow.ac.uk
Abstract
The causes of scale change in schematic maps are introduced and the consequences of these on the use of such maps is discussed. The term ‘scale’ can have many meanings, but in a mapping situation it means the ratio of the actual measurement on the ground and similar measurement on the map. In traditional definitions of maps, it is assumed that to all intents and purposes maps are produced to a fixed scale. While some change of scale is inevitable due to transformation of the curved earth to a flat piece of paper (or computer screen), generally any such change of scale is organised and predictable, with the method of projection chosen to fit the purpose of the map. Schematic maps are attempts to simplify geographical reality, not only by limiting the selection of information shown, but typically focusing on connections between objects rather than their true geographical position, size or shape. This emphasis on topological relationships rather than geography inevitably results in distortions of scale. A key issue in terms of scale and schematic maps is that in many schematic maps the change of scale is not systematic. There may be a general trend, such as enlargement of the central area of the map, but this often far from regular or predictable. This unsystematic changing of scale has often lead cartographers to dismiss many schematic maps for consideration as true maps, but the current ICA definition of ‘map’, probably accepted by most modern cartographers, is more generous in its definition and includes all such graphical representations ‘ … where spatial relationships are of primary importance.’ In principle there are two main reasons for scale change in schematic maps: changes in scale resulting from simplification of the network; and changes in scale to allow areas with more dense information to be seen clearly. In practice, a third reason is manipulation of the network to improve the aesthetics of the design. How scale change is applied in theory and practice is discussed, including consideration of mathematical approaches such as polyfocal projections, spider maps and other techniques. While the majority of schematic maps focus on public transport, there are other maps which also make use of schematisation. The paper reviews how scale changes in a range of examples in different application areas. It then goes on to discuss the impact of scale change on the use of maps, and when this is of consequence to the user. This includes usability issues such as the importance of travel time in transit maps used for journey planning, with examples illustrating approaches to solving this problem.
Keywords
schematic maps; scale; map use