Working with Map Projections

A Guide to their Selection

Fritz Kessler, Sarah Battersby

• Publisher: CRC Press
• Year: 2019
• eBook ISBN: 9781351396059
• Topic: Biological Sciences
• Subtopic: Environmental Science
• Index: Biological Sciences

A map projection fundamentally impacts the mapmaking process. Working with Map Projections: A Guide to Their Selection explains why, for any given map, there isn't a single "best" map projection. Selecting a projection is a matter of understanding the compromises and consequences of showing a 3-D space in two dimensions. The book presents a clear understanding of the processes necessary to make logical decisions on selecting an appropriate map projection for a given data set. The authors discuss the logic needed in the selection process, describe why certain decisions should be made, and explain the consequences of any inappropriate decision made during the selection process.

This book also explains how the map projection will impact the map's ability to fulfill its purpose, uses real-world data sets as the basis for the selection of an appropriate map projection, and provides illustrations of an appropriately and inappropriately selected map projection for a given data set. The authors take a novel approach to discussing map projections by avoiding an extensive inventory of mathematical formulae and using only the mathematics of map projections that matter for many mapping tasks. They also present information that is directly applicable to the process of selecting map projections and not tied to a specific software package.

Written by two leading experts, this book is an invaluable resource for anyone studying or working with geospatial data, from students to experienced professionals, and will help readers successfully weigh the pros and cons of choosing one projection over another to suit a map's intended purpose.

Part I

Projection Basics, Cartographic Symbolization, Projection Influences on People’s Mental Maps, and Selecting Projections

This book is divided into two parts. Part I provides foundational knowledge about map projections, how projections influence people’s world mental maps, considerations necessary when selecting a projection, and the cartographic symbolization process involved when making a map. Collectively, these topics are beneficial background preparation for Part II of the book, where we focus on a detailed discussion of working with and selecting projections for different map symbolization methods.

To begin, we will briefly discuss the four guiding themes from Part I that are important for the reader to review as preparation for examining the material included in Part II.

• 1. General Background on Map Projections. (See Chapter 2 for an overview of projections, what they are, and how they are created.)
• The projection is an inherently mathematical process that takes latitude and longitude values on Earth’s spherical surface and projects them to a map. The projection process can preserve certain spatial relationships that are found on Earth’s surface such as areas, angles, distances, and directions, but it cannot preserve all of these spatial relationships at the same time. Not all projections preserve a specific spatial relationship property, and those that do have limitations in the way the property is preserved. The inability for any given projection to preserve all of Earth’s spatial relationships is due to the change in dimensions from the sphere (Earth, 3-dimensional) to a plane (map, 2-dimensional). This loss of dimension can be described as distortion. Every projection includes distortion and the amount, type, and location of distortion can impact the map’s ability to fulfill its purpose. Thus, you, the map maker, must be familiar with projections, their properties, and their distortion patterns. This knowledge is essential to the process of selecting an appropriate projection that will to support the map’s purpose and lead to an easy to interpret visualization.
• 2. Overview of the Cartographic Process. (See Chapter 3 for a discussion of how phenomena on Earth’s surface are abstracted and symbolized on a map.)
• Earth’s surface is complex and full of details, and a map can only present a simplification and abstraction of that complexity. No map can preserve and display all of Earth’s complexities and details. There within lies the struggle. How can we design maps that capture the essential data from a phenomenon and symbolize it so that it appropriately represents the phenomenon as it exists on Earth’s surface? To overcome this struggle, the map maker begins by conceptualizing how a specific phenomenon on Earth’s surface is distributed, for instance, does it exist everywhere or only in isolated instances (i.e., continuous or discrete), and how does the phenomenon change across space (i.e., abruptly or smoothly). Next, the map maker collects the necessary data to represent the phenomenon as points, lines, or areas. The collected data is described as having a specific measurement level (e.g., qualitative or quantitative). This assignment is needed to select a visual variable that is appropriate for the data measurement level. Specifically, the visual variable helps the map reader intuitively perceive the graphic marks placed on the map to represent the collected data. Next, the map maker selects an appropriate symbolization method (e.g., choropleth, proportional symbol, dot method, isarithmic, dasymetric, or cartogram) that incorporates all the above considerations while representing the phenomenon’s distribution on Earth’s surface. Finally, the map maker identifies the projection that will best highlight the spatial patterns to reflect the original phenomenon being mapped.
• 3. Map Projection’s Influence on People’s Mental Maps. (See Chapter 4 that examines the influence that projections have on people’s mental maps.)
• Everyone has a mental atlas, so to speak. That atlas contains mental maps that reflect the perceived size and shape of the world and its many landmasses. For most people, those maps are constructed according to what they have seen on map, and the projections that the map reader is most familiar with will likely serve as the mental atlas’s framework. As we will discuss in Chapter 2, every projection contains distortion. Thus, the maps that are instrumental in helping construct a person’s mental atlas are distorted and could influence the way the world is remembered and interpreted. This chapter highlights research on how projection may influence mental maps, and how those mental maps are compared to reality.
• 4. Selecting a Map Projection. (See Chapter 5 for an examination of the decisions and trade-offs involved when selecting a projection.)
• Although there are claims to the contrary, there really is no single best projection. Any projection distorts Earth and everything upon it. If you agree with this statement, then you must accept that no one projection is best suited for a given map purpose. In order to select a projection, the map maker must be willing to enter into a give and take relationship; some projection characteristics and parameters will be favorable to support a specific map’s purpose while others will need to be sacrificed.
• When selecting a projection, there are several questions the map maker must ask. Some of these questions focus on the need for the projection to preserve a specific property so the map reader can use the map for a given purpose. Other questions examine the geographic extent of the landmass and data with respect to the distribution of distortion across the map’s surface. Additional questions focus on the aesthetics (e.g., how the overall shape of the projection fits the display space and should the poles be represented as lines or points) and interpretability (e.g., does the inclusion of the graticule provide the map reader with a geographic context when interpreting the map). These questions are discussed at length in this chapter explaining how each impacts the appearance and function of the map.
• Until the advent of computers, there were only a few written guidelines available to recommend a projection. Even so, those guidelines were not very helpful as they expected those using the guideline to have a certain level of projection knowledge. Today, automated projection selection guidelines allow map makers with limited projection knowledge to interactively work through decisions needed to select a projection. The logic of several automated projection selection guidelines will be examined in this chapter.

Readers who are unfamiliar with any of these topics are encouraged to read through Part I before examining Part II. Readers with a sufficient background in the topics covered in Part I can skip ahead and read chapters of interest in Part II. We note that the chapters in Part II were not intended to be read in a particular order; thus, they can be read individually as they present information relevant to your particular map type of interest.

1

Introduction

For most of our professional careers, we (Fritz and Sarah) have worked with, taught, and researched various facets of map projections. We thoroughly enjoy the subject. However, we have come to realize that many people who work with geospatial data need guidance when working with projections on a mapping project. Specifically, we find that many people need help selecting a projection, and that this is a process which is fraught with challenges. Beşdok et al. (2012, p. 666) offer that “map projections are among the most difficult topics” while Muehrcke and Muehrcke (1978, p. 457) go a step further and state that projections are the “most bewildering aspect of map appreciation.”

If you are reading this book, then you most likely work with projections and have found the subject challenging or even bewildering. Projections don’t have to be either; in fact, working with projections can be fun and a rewarding part of making maps. We hope that reading this book will help demystify the challenges you may face when working with projections. To do this, we present five themes that describe the common challenges that people face when working with projections. These themes helped organize our thoughts when writing this book. First, projections are inherently mathematical. Second, projection terminology is filled with confusing jargon. Third, the projection literature is scattered. Fourth, the projection is often overlooked as a variable in the map design process. Fifth, selecting a projection is not a clear-cut process. We will briefly discuss each of these themes here, and we have also woven them into the discussion throughout this book.

Mathematical Complexity

Projections are inherently mathematically based, and this can make the topic intimidating to many. In fact, John Snyder (1993, p. 276) once stated “working with projections still strikes fear in the hearts of many trained cartographers and geographers because of the mathematical aspects.” For those readers who are familiar with mathematics (primarily calculus and differential equations) books are available that may enlighten your mathematical understanding of projections. However, we suspect that for most readers learning about the mathematics of projections is scary and viewed as not necessary. To some ...

Table of contents

• Cover
• Half-Title
• Title
• Copyright
• Dedication
• Contents
• Preface
• Acknowledgements
• Authors
• Part I Projection Basics, Cartographic Symbolization, Projection Influences on People’s Mental Maps, and Selecting Projections
• Part II Projection Selection by Map Type
• Appendix
• Bibliography
• Index