Introduction to Georeferencing

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Questions and Answers

Which of the following best defines georeferencing?

The process of associating data with a specific location on Earth using coordinate systems (correct)

Determining the exact time a location was created

The process of measuring distances on the Earth's surface

The ability to project 3D objects onto 2D surfaces

Geographic Coordinate Systems can accurately compute areas and distances.

False

What is the range of longitude values?

from 0° at the Prime Meridian to ±180°

The ____ projections preserve area but distort shape.

Equal-Area Signup and view all the answers

Match the following projection types to their properties:

Equal-Area = Preserves area but distorts shape Conformal = Preserves shape but distorts area Equidistant = Preserves distances in specific areas True-Direction = Preserves angles and directions Signup and view all the answers

Which term refers to a line of constant latitude?

Parallel Signup and view all the answers

All map projections equally preserve area, shape, and distance.

False Signup and view all the answers

What is the purpose of map projections?

To convert Earth’s 3D surface into a 2D map. Signup and view all the answers

Which map projection preserves area but distorts shape, distance, and direction?

Albers Equal Area Signup and view all the answers

The Orthographic projection simulates viewing the Earth from its center.

False Signup and view all the answers

What type of coordinate system divides the globe into 60 zones, each 6° wide?

Universal Transverse Mercator (UTM) Signup and view all the answers

The ________ projection is known for preserving distances and directions from a central point.

Azimuthal Equidistant Signup and view all the answers

Match the following map projections to their properties:

Lambert Conformal Conic = Preserves shape and direction; distorts area Mercator = Preserves direction and shape; distorts area at high latitudes Albers Equal Area = Preserves area; distorts shape, distance, and direction Azimuthal Equidistant = Preserves distances and directions from a central point Signup and view all the answers

Which projected coordinate system uses meters for coordinating locations?

Universal Transverse Mercator Signup and view all the answers

The State Plane Coordinate System is designed to minimize distortion across the globe.

False Signup and view all the answers

What is the main difference between a Geographic Coordinate System (GCS) and a Projected Coordinate System (PCS)?

GCS is based on latitude and longitude and is unprojected, while PCS is projected and allows accurate distance, area, and direction measurements. Signup and view all the answers

Study Notes

Introduction to Georeferencing

Georeferencing associates data with a specific location on Earth using coordinate systems
Enables geographic information systems (GIS) to accurately map features

Key Properties of Georeferencing Systems

Uniqueness: Locations must be uniquely identifiable, like differentiating locations with the same name (e.g. Springfield, MO vs Springfield, UK)
Persistence: Locations remain consistent over time
Spatial Resolution: Specifies level of detail (e.g. "Norman" is more precise than "Oklahoma")
Metric vs. Non-Metric:
- Metric: Uses coordinate systems for distance calculations (e.g., latitude/longitude)
- Non-Metric: Uses relative locations (e.g., "next to the river")

Geographic Coordinate System (GCS)

Uses latitude and longitude lines to define locations
Components:
- Latitude (Parallels): Measures north-south position, ranging from 0° at the equator to ±90° at the poles
- Longitude (Meridians): Measures east-west position, ranging from 0° at the Prime Meridian (Greenwich, England) to ±180°
Units: Angular degrees, minutes, and seconds (or decimal degrees)
- Example: Norman, Oklahoma = 35°13'N, 97°26'W
Terms to Remember:
- Meridian: Line of constant longitude
- Parallel: Line of constant latitude
Unprojected Nature of GCS: Cannot accurately calculate areas or distances without projection

Map Projections

Converts Earth's 3D surface to a 2D map
Introduces distortions

Projection Properties

Equal-Area (Equivalent): Preserves area, but distorts shape
Conformal (Orthomorphic): Preserves shape, but distorts area
Equidistant: Preserves distances (only in specific areas)
True-Direction (Azimuthal): Preserves angles/directions
Compromise: Balances distortion among properties

Projection Factors

Developable Surfaces: Shapes onto which Earth is projected
- Cylindrical: Gridlines form rectangles (e.g., Mercator)
- Conical: Gridlines curve (e.g., Albers Equal Area)
- Planar: Gridlines radiate from a central point (e.g., Azimuthal)
Aspect: Orientation of the developable surface
- Normal: Aligned with the poles
- Transverse: Aligned with the equator
- Oblique: At an angle
Viewpoint: Light source for projection
- Gnomonic: From the Earth's center
- Stereographic: From the far side of the globe
Case: Intersection of developable surface with Earth
- Orthographic: From infinity
- Tangent: Touches at one line or point
- Secant: Cuts through the Earth

Common Map Projections

Albers Equal Area: Preserves area, distorts shape, distance, and direction; Conic projection; used for regional/national maps
Lambert Conformal Conic: Preserves shape and direction, distorts area; Conic projection; used for navigation, State Plane Coordinate System
Mercator: Preserves direction and shape; distorts area at high latitudes; Cylindrical projection; used for navigation, world maps

Projected Coordinate Systems (PCS)

Grid superimposed on a map projection, specifying locations in a plane
Components:
- Ellipsoid: A mathematical model of Earth's shape (e.g., GRS80, WGS84)
- Datum: Links ellipsoid to specific Earth locations (e.g., NAD83)
- Projection: Converts 3D Earth to 2D coordinates
Common PCSs:
- Universal Transverse Mercator (UTM): Divides globe into 60 zones, uses meters for coordinates, popular for GPS mapping
- State Plane Coordinate System (SPCS): Divides states into zones, uses different projections to minimize distortion (Lambert or Mercator)

Practical Applications

GCS vs. PCS:
- GCS (latitude/longitude) is suitable for global contexts
- PCS (projected) allows accurate distance, area, and direction measurements
Choosing the right projection depends on map purpose
- Preserve area for population density
- Preserve distance for transportation
- Preserve direction for navigation

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Description

Explore the fundamentals of georeferencing, which links data to specific locations on Earth through various coordinate systems. This quiz covers key properties, geographic coordinate systems, and the significance of spatial resolution in mapping. Test your knowledge of GIS and its components!