Thematic Cartography, Thematic Cartography and Transformations

Colette Cauvin, Francisco Escobar, Aziz Serradj

• Publisher: Wiley-ISTE
• Year: 2013
• Print ISBN: 9781848211100
• eBook ISBN: 9781118619513
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Geography
• Index: Geography

A thematic map is a map that illustrates more than simply geographical relationships or locations, but rather also portrays themes, patterns, or data relating to physical, social, medical, economic, political, or any other aspect of a region or location. Examples include maps that show variations of population density, climate data, wealth, voting intentions, or life expectancy with geographical location. These tools have become central to the work of scientists, practitioners, and students in nearly every field, from epidemiology to political science, and are familiar to members of the public as a common means of expressing complicated and multivariate information in easily understood graphical formats.

This set of three volumes on Thematic Cartography considers maps as information constructs resulting from a number of successive information transformations and the products of decision stages, integrated into a logical reasoning and the order of those choices. It thereby provides a thorough understanding of the theoretical basis for thematic mapping, as well as the means of applying the various techniques and methodologies in order to create a desired analytical presentation.

This first volume introduces the basics of thematic cartography. The authors present the transformations necessary to the production – using a scientific approach – of any thematic map. Four stages are detailed: from geographic entities to cartographic objects; the [XY] transformation; the [XYZ] cartographic transformations; and the semiotic transformation. Technical aspects giving map-reading keys are also included.

PART I

Cartography: An Evolving Scientific Discipline

Part I

Introduction

We pointed out earlier that mapmaking should follow very precise minimal rules in order for the final document to be a scientific construction and not only an author’s illustration accompanying a text. These rules act on all stages of the cartographic production, and the “products” should be created using a recognized scientific approach which consists of several connected steps. Researchers generally invest in one or other of these stages, foregoing the logical process in the production of a map. However, none of the stages is independent from the others, and disregarding the links between them can only result in maps which are unsatisfactory in many aspects. There is a need to establish a scientific approach.

In fact, the rules of mapmaking should not be limited to graphical expression. They should act in all the phases of cartographic production. Nevertheless, while this idea has already been recognized and partially explained [CAU 96a, CAU 98], its structuring and generalization are exigent today for at least three reasons: the proliferation of computer software, the diversity of specialists and the absence of a structured theoretical body of knowledge.

The proliferation of computer programs for cartography or for geographical information systems requires a harmonization of tools and a determination of their real innovative quality. This (over)-abundance in fact makes anyone capable of somehow producing a map by using the functions of a program, regardless of its validity, without even knowing whether the chosen technique can be applied to the data at hand, whether it is new or whether it has been tested before. This common ignorance is the reason for sketching the history of cartography in the first chapter, in order to avoid errors and consider as new the techniques which have been in use for several centuries.

The diversity of specialists in map production creates the need for a harmonized vocabulary, because the increasing number of specialties produces a simultaneous increase in the number of new terms and unheard-of possibilities which must be coordinated and unified for the sake of correct usage. It is sufficient to recall the phrase by Epicurus addressed to Herodotus to understand the necessity of a precise and explained vocabulary, even if it is only a vocabulary of work: “In the first place, Herodotus, you must understand what it is that words denote, in order that by reference to this we may be in a position to test opinions, inquiries, or problems, so that our proofs may not run on untested ad infinitum, nor the terms we use be empty of meaning” [EPI 98]. Thus, Chapter 2 will deal with the definitions of the terms used in explaining the adopted choices and points of view.

The absence of a structured theoretical body of knowledge is manifest in the absence of thought-through and coordinated scientific principles applied to the stages of the cartographic conception and production. Evidently, a theoretical body of knowledge is vital for the development of any scientific discipline. Hence, only the formation of such a body will allow cartography to fully exploit its potential, and allow the map to demonstrate the directly observable thematic phenomena as well as reveal the underlying spatial structures which contribute to their understanding. Cartographic construction and geospatial analysis are inseparable in understanding these structures and demonstrating the corresponding processes. Therefore, maps must be made using the rigorous approach described in Chapter 3 if we want a map to be reproducible and to serve as an object of experiments and/or of demonstration in understanding a spatial phenomenon.

To conclude, a map cannot be produced for the sake of producing a map. Mapmaking should be justified; otherwise it is a waste of time both for its author and its user. A map is a logical construction, and the logic on which it is based is two-fold: that of the topic of the map and that of cartography. The disciplinary and the cartographic logic fit together and rely on the experimental scientific approach which makes sure that each step can be verified, explained and discussed. This approach, therefore, is an indispensable guide.

Chapter 1

A Brief History of Thematic Cartography

“One needs to know history to avoid thinking that certain things are new”, maintain M. Friendly and D. J. Denis [FRI 04]. This statement is essential in our time when many authors announce such “discoveries” and emphasize the originality of a map they produced, without having a single argument to support their claims. Cartography is ancient, perhaps even preceding writing [ZUM 93]. If we want to avoid mistaking some maps for discoveries, knowing the history of this discipline, just like any other, is essential. It allows us to put into perspective the real importance of maps produced in our time, to understand better the social context in which they have been created and thus to avoid errors of interpretation.

1.1. From cartography to thematic cartography

Originally, cartography responded to concrete needs, and maps – the output of cartography – were developed for practical reasons. For example, they served to define the boundaries of land property, as with the cadastral plans on clay Mesopotamian tablets from around 2500 BC [JAC 92], to find one’s bearings, as with the road maps in the Roman era (the Peutinger table, 2nd century AD), or to determine the course at sea, using vellum nautical maps. A map can also serve as an archive of knowledge of a group of people [ZUM 93]. In the beginning, therefore, cartography was first and foremost aimed at positioning places relative to each other, and precise locations remained uncertain. It gradually became more precise thanks to the great discoveries, inventions in different domains and technological advances. These advances took place in the cultural and social context of varying degrees of openness to change.

1.1.1. The Middle Ages in the West: symbolic maps

During the early Middle Ages in the Western world, maps were mostly figurative and symbolic, expressing the ideas of the time, i.e. religious ideas, since “symbols reflect the way we interpret them through the prism of the culture of the time and religious beliefs” [ZUM 93]. These maps were a complete departure from the ideas proposed by Ptolemy. At the time, the scientific approach of a real world depiction was abandoned in favor of figurative, Bible-related imagery and religious beliefs. The famous “T-O” maps abounded, with a ring (“O”) of ocean encircling the world, inside which there is a “T”, separating the space into three parts: Asia at the top (corresponding to the East), Europe on the left and Africa on the right [LEF 04].

In this period, only Arab cartography, which acknowledged and continued Greek work, drawing mainly on Ptolemy, advanced thanks to the geographers, travelers, and writers such as Masudi and Ibn Haukal in the 10th century, Edrisi (or al-Idrisi) in the 12th century, and Ibn Batuta and Abufelda in the 14th century [CUE 72, LEF 04]. It is also thanks to these Arab researchers and writers that the compass, the instrument devised by the Chinese a few centuries earlier, arrived in the West around the 13th century and caused a major change in mapmaking with the appearance of portolans. The recognition of Ptolemy’s work allowed a departure from figurative imagery, to correct the flagrant errors and to expand the content of the map, even if some new errors were introduced on the way, since Ptolemy in his time did not possess all the necessary information. For instance, the size ascribed to Eurasia and the calculated length of the equator made the existence of America completely impossible [ZUM 93].

1.1.2. From the Renaissance to the 19th century: resurgence of cartography due to discoveries and innovations

During the Renaissance, innovations emerged in a variety of fields, some of which would play an essential role in cartography. The improvement in measuring instruments allowed advancements in surveying the Earth. Developments in mathematics led to a much more precise depiction of projected information. The blossoming of techniques due to the introduction of new tools induced a genuine revolution in the design, as well as the printing and distribution, of maps (Figure 1.1).

Figure 1.1. Innovations and resurgence of cartography

The end of the 15th and the 16th century is a period marked, at least in the West, by the great discoveries which helped update, modify and correct cartographic documents. Knowledge of the Earth had increased considerably with the voyages of Christopher Columbus (1492–1502), Vasco de Gama (1497–1524), Magellan (1519–1522) and others. New techniques caused major changes in mapmaking: the introduction of paper in Europe thanks to the Arabs between the 11th and 14th centuries, the invention of the printing press (or rather, of typesetting) by Gutenberg (1440), with the first map printed in 1472, and switching from wood engraving to copper engraving devised by Finiguerra (1452), which enables much finer details to be depicted. The 16th century is punctuated with discoveries and inventions which revolutionized the knowledge of the Earth and cartography. G. Palsky [PAL 01], M. Friendly and D. J. Denis [FRI 04] agree in stressing the importance of new instruments, which allowed more precise observations and corrected measurement errors. The first planimetric surveys made with a compass and cord [CUE 72] were developed at the same time as the new projection systems, in particular, the Mercator (1512–1594) and the Ortelius (1527–1598) projections.

In the 17th century, cartography continued to be marked by technological innovations. Thus, optical instruments, conceived by Galileo with the creation of the first high quality telescope in 1609, allowed the execution of fine details on a map and a considerable improvement in the quality of the fieldwork [CAH 74], and thereby “propelled geography and cartography into modernity” [ZUM 93]. These advances were crowned by repeated application of the triangulation technique invented in 1533 by a physician, geographer and mathematician G. Frisius, which led to the complete coverage of France by the Cassini family (17th and 18th centuries). Some of the ministers of Louis XIV were strongly interested in maps, which were becoming more reliable and had practical uses. Geographical maps were requested from the Academy of Sciences created by Colbert in 1666, while the royal corps of engineers supplied maps to Louvois (French Secretary of State for War during the reign of Louis XIV). Efforts were being made toward improvements in surveying and also in accuracy of data. At the end of the century, these efforts extended to the revision of latitudes and longitudes, as well as measurements of the Earth [CUE 72]. Similar efforts were evident in other countries: in Russia, Peter the Great established the teaching of geodetics, while in England topographic surveying was also carried out [CUE 72].

Other new techniques concerning the accuracy of measurements, drawing, as well as the reproduction and distribution of maps, came about in the following centuries. For instance, there were new measurements of the meridian arcs at the equator and at the poles [CUE 72], and an increase in number of projection systems brought about by Bonne, Gauss and Lambert [ALI 66]. The 18th century saw the invention of the chronometer1 by Harrison in England (1734), the adoption of the metric system during the French Revolution (1791), the completion of the Cassinis’ topographic map with 1/86,400 scale and the design of the first machine for the continuous manufacture of paper by Louis-Nicolas Robert (1798).

The emergence of lithography (1796) would lead in the 19th century to the production of maps in several colors, which, from that time on, would be obtained via mechanical processes such as chromolithography in the 1840s [PAL 02]. At the end of the same century, the invention of photography by Niepce (1822) began to be used in cartography. From then on, photographic reproduction offered an opportunity to draw maps without inversion. Offset printing, invented in 1878, was put into use around 1910 [CAH 74].

1.1.3. The 20th century: widespread acceleration

In the 20th century, the pace of change accelerated due to an ongoing proliferation and diversity of technological advances concerning chemistry, electronics, the processes of drawing, printing, visualization and distribution, as well as the types of data used. Aerial photography, whose fu...

Table of contents

• Cover
• Dedication
• Title Page
• Copyright
• Foreword
• General Introduction
• Part I: Cartography: An Evolving Scientific Discipline
• Part II: Data Construction: A Transformation Defining the Quality of the Map
• Part III: Necessary Transformations in Thematic Cartography
• General Conclusion
• Bibliography
• Software Used
• List of Authors
• Summary of Other Volumes in the Series
• Index