Projections, Coordinate Systems, and GPS Technology in Geospatial Analysis

What is a map projection?

A method for representing the curved surface of the Earth on a flat map.

What are the main types of map projections?

Cylindrical, conical, and planar.

What does a conformal projection preserve?

Shape and angles.

What is the Universal Transverse Mercator (UTM) system?

A global map projection system divided into 60 zones, each with minimal distortion.

What is the purpose of the State Plane Coordinate (SPC) system?

To provide a unique coordinate system for each state or portions of a state.

What are the properties of UTM coordinates?

Conformal shape preservation, accurate area representation, and minimal distortion within each zone.

What is trilateration in GPS?

A method that uses measurements from at least four satellites to determine a position.

What is the role of the fourth satellite in trilateration?

To help reduce timing errors.

What are common sources of error in GPS measurements?

Receiver design, satellite positions, atmospheric conditions, and human error.

What is Differential GPS (DGPS)?

A method that uses ground-based correction to improve GPS accuracy.

What is the Wide Area Augmentation System (WAAS)?

A system that corrects GPS signal errors caused by atmospheric disturbances.

What is Selective Availability (S/A) in GPS?

A government policy that intentionally degrades GPS accuracy to prevent hostile use.

What does GIS stand for?

Geographic Information System.

What is the primary function of GIS?

To store, analyze, and visualize geographic data.

What is remote sensing?

The acquisition of data about the Earth's surface from satellites or aircraft.

What applications use remote sensing technology?

Urban planning, environmental monitoring, public health, and military intelligence.

What is the space segment of GPS?

The satellites and the signals they broadcast from space.

What is the control segment of GPS?

The control stations that monitor and manage the GPS satellites.

What is the user segment of GPS?

The GPS receivers that pick up signals from the satellites.

What is the purpose of the GNSS constellation?

To ensure coverage and communication with multiple satellites regardless of location.

What are some other Global Navigation Satellite Systems (GNSS) besides GPS?

GLONASS (Russia), Galileo (EU), BeiDou (China), NAVIC (India), QZSS (Japan).

How is distance calculated in GPS?

By measuring the time it takes for satellite signals to reach the receiver.

What is the significance of the ephemeris in GPS?

It contains data about satellite orbits and helps correct positional errors.

How many satellites are needed for full coverage?

24

DGPS

differential GPS - method using a ground-based correction in addition to the satellite signals in position determination

CORS

Continuously Operating Reference Stations; a system operated by the National Geodetic Survey to provide a ground-based method of obtaining more accurate GPS positioning

SBAS

satellite-based augmentation system; a method of using correction information sent from an additional satellite to improve GPS position determination

WAAS

Wide-Area Augmentation System: Corrects for GPS signal errors caused by ionospheric disturbances, timing, and human error

Datum

A mathematical model of earth used as a reference for locating geographic positions

GCS

Geographic Coordinate System: Uses latitude and longitude on a curved surface

What shape is the earth?

ellipsoid

Great Circle Distance

the shortest distance between two points on a spherical surface

Mercator

Cylindrical map projection that preserves shape

Albers Equal Area

Conic projection that preserves the area

Azimuthal equidistant

Preserves distance/direction from the center point

Planar

Reference surface projected onto a plane

false easting and northing

arbitrary values added to x and y values; usually used to ensure that all x-y coordinates are positive