Making Maps Easy to Read

RELIEF: DEPICTING A SURFACE ON A MAP

This part of the research project was concerned with relief maps and the best way to show a three-dimensional surface on a map.

Introduction
Four Types of Relief
Computer Maps
Contour Lines
Layer Tints
Overview & Experimental Method


Introduction

Relief is one instance of the general problem of showing a three-dimensional surface on a map; the problem of showing hills and valleys is not substantially different from that of representing a statistical surface such as the rainfall distribution. People are notoriously poor at reasoning in three dimensions and so it is no surprise that many people find relief harder to interpret than most other information on a map. There are more than a dozen distinct methods for showing relief and so the map designer has a wide choice. We have conducted a series of experiments to discover how different methods affect map reading performance. Our approach differs from previous research in assuming that a number of different map reading tasks must be used in an experiment and that the best method of showing relief may depend on the way the map is to be used.

As well as providing cartographers with information about performance, we have attempted to understand some of the more important processes in relief map interpretation. One approach to this has been to use cluster analysis to group together similar map reading tasks.

One important factor in relief interpretation is the memory load in integrating information from different parts of the map. A successful relief map, among other things, reduces the load on memory, for example, by making good use of peripheral vision.


Four Types of Relief

This experiment compared four types of relief map: layer tints, contours, contours with hill shading, and digits.


The best choice of map depends strongly on what the map reader is asked to do. This chart provides a very much simplified picture of the results: see the paper for fuller details.

Reference -
Phillips, R. J., De Lucia, A. and Skelton, N. (1975). Some objective tests of the legibility of relief maps. Cartographic Journal, 12, 39-46.

Abstract - The legibility of four different types of relief map (contours, contours with hill shading, layer tints and digital or spot height maps) was compared using 13 different map reading test questions administered to 179 subjects. Many of the questions showed large and statistically significant differences between the four types of map, but no single type of map was best for all purposes. The results demonstrate that the choice of an appropriate relief map has a very real effect on the map reader's performance, and that this choice must depend on the way the map is to be used.

Full paper as pdf file (1529KB).


Computer Maps

Here are examples of the four types of computer-generated relief maps: two 'vu' maps, 'layer' and 'contour'. They were compared by means of map reading tests.


This chart gives a crude summary of how the computer-generated relief maps performed on different types of map reading task. See the paper for a fuller picture.

Reference -
Phillips, R. J. and Noyes, L. (1978). An objective comparison of relief maps produced with the SYMAP and SYMVU programs. Bulletin of the Society of University Cartographers, 12, 13-25.

Abstract - 123 university students answered a series of questions which measured their speed and accuracy in using relief maps produced by the computer programs SYMAP and SYMVU. Most questions produced statistically significant differences between the four types of map investigated and, on all of these, a layer version of SYMAP was superior to two types of SYMVU map. It appears that the pictorial appeal of SYMVU is misleading and that a layer version of SYMAP is better for extracting information. In general, the results are consistent with a previous experiment which tested conventional relief maps.

Full paper as pdf file (1368KB).


Contour Lines


This 'wedding cake' elaboartion of contour lines should help map readers make judgments about relative height because it removes ambiguity about the direction of slope. But map reading tests showed no improvement over conventional contour lines.

Reference -
Phillips, R. J. (1979). An experiment with contour lines. Cartographic Journal, 16(2), 72-76.

Abstract - Map readers are generally faster and more accurate in interpreting relief from layer tint maps than from contour maps. This paper discusses methods of improving contour maps and reports an experiment where conventional contours were compared with contour lines elaborated to produce a 'wedding cake' effect, but this elaboration did not improve performance. The main problem for adults when reading contour maps may be a difficulty in integrating small areas of relief in order to visualise a larger area. If this is correct, no simple elaboration of contour lines will help the map reader unless it gives contours the conspicuity which layer tint colours have in peripheral vision.

Full paper as pdf file (802KB).


Layer Tints

Map reading tests were used to compare four types of layer tinting for use in school atlases.

Reference -
Phillips, R. J. (1982). An experimental investigation of layer tints for relief maps in school atlases. Ergonomics 25 (12) 1143-1154.

Abstract - English teenage school children carried out some representative map-reading tasks to evaluate layer tints for use in school atlases. Two spectral colour schemes (loosely following the colours of the spectrum) were compared with two tonal schemes (varying tone, constant hue). Judgements of absolute height were carried out more accurately on the spectral maps, but judgements of relative height were better with the tonal maps. Other questions involving the map base and visualisation of the relief showed no reliable differences between the maps. Spectral schemes have the disadvantage that colours are difficult to order correctly. The problem with tonal schemes is that colours are often hard to discriminate. Innovative design may overcome both these problems but given the alternatives considered here, the tonal maps seem preferable as relative height is more important than absolute height for children using atlases.

Full paper as pdf file (1150KB).


Overview & Experimental Method

Reference -
Phillips, R. J. (1984). Experimental method in cartographic communication: research on relief maps. Cartographica 21(1), 120- 128.

Abstract - This paper considers the use of tests of performance based upon map readers' speed and accuracy to evaluate relief maps. It briefly discusses some results which have been obtained from this approach. The process of creating a mental image from a relief map is seen as a data reduction task with the greatest information load occurring in the early stages of visual processing. It is argued that changes in map design will have their greatest effect in these early stages. The advantages and difficulties of testing are discussed and some recommendations are made for designing experiments which test relief maps.

Full paper as pdf file (1.00MB).


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Updated 19 August 2003