Map Projections

Summary

This presentation offers a comprehensive overview of map projections, exploring their surfaces, coordinate grids, and datums. It highlights the challenges of representing the Earth's 3D surface on a 2D map, introducing key concepts like the Mercator projection and its distortions. The script delves into the importance of datums, such as WGS84 and NAD83, and their role in map accuracy. It also explains the use of different projection types, like cylindrical, conical, and azimuthal, and concludes with an introduction to UTM (Universal Transverse Mercator), emphasizing its military and practical applications.

Takeaways

• 😀 Map projections represent the Earth's 3D surface on a 2D plane, always with some distortion.
• 😀 There is no 'perfect' map projection, as different projections prioritize different characteristics like area, shape, or distance.
• 😀 The Mercator projection, created in 1569, is widely used for navigation, but it distorts areas near the poles, making Greenland appear much larger than Africa.
• 😀 Cylindrical, conical, and azimuthal are the three main types of projection surfaces, each with different characteristics.
• 😀 The Mercator projection is a cylindrical projection, where the globe is projected onto a cylinder. Distortions increase away from the equator.
• 😀 The choice of projection surface (cylinder, cone, or plane) determines how meridians and parallels are represented.
• 😀 A coordinate system of latitude and longitude is used on maps, with the Prime Meridian historically passing through the Canary Islands.
• 😀 The current Prime Meridian is based on the Greenwich Meridian, but the WGS84 system uses a slightly shifted reference point due to satellite technology.
• 😀 The Earth’s shape is not a perfect sphere, but rather an uneven, bumpy shape, measured by the geoid, which is the reference for map projections.
• 😀 A datum defines the Earth's model and includes an ellipsoid, geoid, and reference points. WGS84 is the most commonly used datum, especially for GPS systems.
• 😀 UTM (Universal Transverse Mercator) is a coordinate system using a transverse Mercator projection and divides the Earth into 60 zones, each with its own projection.

Q & A

Who was the first to prove the Earth was not flat and measure its circumference accurately?

The Greek scientist and father of geography, Eratosthenes, was the first to prove that the Earth was not flat and accurately measured its circumference before he died in 194 BC.

What is a map projection?

A map projection is a method of representing the Earth's three-dimensional surface on a two-dimensional plane. This process inevitably involves distortions, and different projections prioritize different characteristics like area, shape, or distance.

Why is the Mercator projection so widely used despite its distortions?

The Mercator projection, created in 1569 by Gerardus Mercator, was designed for navigation at sea. While it distorts areas near the poles, it maintains accurate shapes and angles, making it useful for maritime navigation.

How does a cylindrical projection work?

In a cylindrical projection, the globe is projected onto a cylinder. This involves imagining a light source inside the globe, projecting the Earth's features onto the cylinder, which is then unwrapped to create a flat map.

What is the difference between a transverse cylindrical and an oblique cylindrical projection?

A transverse cylindrical projection aligns the cylinder horizontally with the globe, whereas an oblique cylindrical projection positions the cylinder at an angle to the globe.

What are the characteristics of an azimuthal projection?

An azimuthal projection uses a plane to project the Earth's surface, producing straight meridians radiating from a point. The parallels of latitude are shown as complete circles centered on the pole.

What is the significance of the Prime Meridian in map projections?

The Prime Meridian serves as the reference point for longitude. It was historically based on a meridian through the Canary Islands, but the modern Prime Meridian is based on the Royal Observatory in Greenwich, England.

Why did the Prime Meridian location change with the introduction of WGS84?

The Prime Meridian shifted slightly with the introduction of the World Geodetic System 1984 (WGS84) due to satellite technology. WGS84 defines the Earth's center of mass, which is more accurate for satellite-based systems, as opposed to the surface-based reference used earlier.

What is the role of a datum in map projections?

A datum is a reference system that provides the foundation for map projections. It includes a model of the Earth's shape (geoid and ellipsoid) and coordinates based on specific reference points on Earth's surface.

What is the UTM (Universal Transverse Mercator) coordinate system?

The UTM system is a projection and grid system used to divide the world into 60 zones, each about 6 degrees wide in longitude. It uses the transverse Mercator projection, where scale is true along the central meridian of each zone, providing accurate coordinates for large-scale maps.