Projections and Coordinates: Turning a 3D Earth into Flatlands
Figure 1. High plains near Chaco Canyon, NM. Even plains have curvature to them, but that curvature is not that significant when mapping an area the size of a large city.Copyright 2003 Stock.xchang http://www.sxc.hu/photo/56952
Projections and coordinates are key advancements in the geographic sciences that help us to better understand the nature of the Earth and how to describe location. These innovations in describing the Earth are the basis for everything that is done in a GIS framework. Shape of the Earth is a critical starting point because in fact the Earth is not round, but rather a more complex shape called a geoid. Coordinate systems are often referenced to a particular model shape of the Earth, but many different formats exist because not all coordinates work equally well in all areas. While projections and coordinates are abstract concepts in themselves, students eventually find them interesting because 1) it causes them to challenge their current ideas of the Earth's shape, and 2) it is much easier to visualize these ideas for learning through interactive GIS such as Google Earth.
Just as a geographic information system (GIS) is an important tool for many engineering applications, so are projections and coordinate systems. Without these tools, GIS would not be possible. Coordinate systems and projections are themselves engineered and continue to be designed so that Earth's surface can be more accurately represented for project design, communication and engineering modeling.
After this lesson, students should be able to:
- Describe the true shape of the Earth, that it is more than simply "round."
- Explain the difficulty of trying to make a rounded object exist in a flat map space.
- Articulate the reality that all flat maps of the globe are flawed in some way and be able to discern what those compromises might be. Be able to list common ways in which maps alter reality in their representation of space.
- Identify the important components of any geographic coordinate system—a value for every spatial dimension, a designation that is unique to every location within the system.
- Explain that coordinate systems are just designed systems. Any number of coordinate systems can be generated or used, though they have various strengths and weaknesses.
- Explain how latitude and longitude relate to the curved Earth surface as angles.
- Explain how engineers apply coordinate systems to map various surfaces.