Introduction to GIS Cartographic Principles

Introduction to GIS Cartographic Principles

• Geodesy is the scientific discipline that determines the size and shape of Earth.
• Early maps depicted a flat Earth, but Aristotle (384-322 BC) argued for a spherical shape.
• Aristotle calculated Earth's circumference to be 45,500 miles (approximately 24,902 miles).
• Eratosthenes (around 250 BC) used the angles of the sun's rays to estimate Earth's circumference, arriving at a comparable value (approximately 25,000 miles).
• Modern measurements show that Earth is not a perfect sphere, it is an oblate spheroid, slightly flattened at the poles and bulging at the equator.
• The NAVSTAR GPS satellites accurately determine Earth's shape.
• A geoid represents a smoothed representation of Earth's topography on top of an ellipsoid.
• Map projections convert a three-dimensional (3D) sphere or ellipsoid to a two-dimensional (2D) flat representation. This transformation always results in some distortion.
• The choice of projection depends on the desired accuracy.

Presentation Outlines

• Geodesy and size of Earth
• Map Projections
  • What is a projection?
  • Distortion of map presentation
  • Planar projections
  • Conical projections
  • Cylindrical projections
  • Reasons for using projections
• Coordinates: a 2D mapping framework
• Issues with map projections - The Problem of Curvature of Earth
• Types of Map Projections
  • Azimuthal/Planar Projections
  • Conic Projections
  • Cylindrical Projections
  • Equal-Area Projections
  • Conformal projections
• Common properties of projections
  • Equidistant
  • Equal Area
  • Orthomorphic/Conformal
• Summary
• Practical considerations

Mapping Framework

• Maps are 2D representations of a 3D Earth.
• Locating positions on Earth involves a 2D coordinate system.
• Easting and northing are used to locate locations across the Earth surface.
• Elevation (the third dimension) is often included relative to a datum. (Mean sea level).

Map Projections

• Map projection: a mathematical process to transfer Earth's features from a sphere ( or ellipsoid) onto a flat surface.
• Projections cause distortion.
• Choosing an appropriate projection is important, as different projections will provide different levels of accuracy for various map elements.
• Common projections methods include planar, cylindrical and conic.

Distortion of Map Presentation

• Distortion represents inaccuracies in angles, shapes, distances, and areas when transferring a curved surface (Earth) to a flat surface (map).
• Every projection has a unique distortion pattern.
• Understanding and minimizing distortion is crucial in cartography.
• Methods used include cones and cylinders to create surfaces with zero curvature.

Problem of Curvature of The Earth

• The Earth's curved surface presents a challenge for mapping.
• Transferring this curvature to a flat map always results in some degree of inaccuracy (distortion) in distance, direction, area or shape.

Unavoidable Distortion

• All map projections inevitably distort the true shape of the Earth.
• Distortion can affect conformity (consistency of scale), shape, direction, area, and scale relative to the curved surface of the Earth.

Summary

• Geodesy has a complex history, with early attempts to map Earth being inaccurate due to flat Earth assumptions.
• Earth shape is usually approximated as an oblate spheroid (ellipsoid) for mapping.
• Map projections transform a 3D Earth to a 2D map, leading to inherent distortions.
• Projections can be planar, cylindrical, or conical.
• All projections introduce some degree of error.

This quiz explores fundamental concepts in GIS cartographic principles, including the history of Earth's measurements and different types of map projections. Understanding geodesy and the implications of Earth's shape on cartography is crucial for accurate mapping and geospatial analysis.