Chapter 1 outlined several of the distinguishing properties of geographic information. One of these properties is that geographic maps are necessarily generalized, and that generalization tends to vary with scale. This chapter will introduce another distinguishing property related to the measurement and display of geographic information: that the Earth's complex, nearly-spherical but somewhat irregular shape complicates efforts to specify exact positions on the Earth's surface. In this chapter, we will explore the implications of these properties by illuminating concepts of scale, Earth geometry, coordinate systems, and the "horizontal datums" that define the relationship between coordinate systems and the Earth's shape.
Compared to Chapter 1, Chapter 2 may seem long, technical, and abstract, particularly to those for whom these concepts are new. Chapter 2 will introduce some of the more technical concepts that are relevant to map construction and map reading. Students who successfully complete Chapter 2 will be able to:
- understand the concept of map scale and the multiple ways it is specified;
- demonstrate your ability to specify geographic locations using geographic coordinates;
- convert geographic coordinates between two different formats;
- explain the concept of a horizontal datum;
- recognize the kind of transformation that is appropriate to geo-register two or more data sets;
- describe the characteristics of the UTM coordinate system, including its basis in the Transverse Mercator map projection;
- describe the characteristics of the SPC system, including map projection on which it is based;
- interpret distortion diagrams to identify geometric properties of the sphere that are preserved by a particular map projection;
- classify projected map graticules by projection family.
Table of Contents:
- What is Scale?
- The Need for Coordinate Systems
- What are Map Projections?
- The Nearly Spherical Earth
Chapter lead adapter: Raechel Bianchetti.
Portions of this chapter were drawn directly from the following text:
Joshua Stevens, Jennifer M. Smith, and Raechel A. Bianchetti (2012), Mapping Our Changing World, Editors: Alan M. MacEachren and Donna J. Peuquet, University Park, PA: Department of Geography, The Pennsylvania State University.