Overview

The foundational concepts are elementary building blocks and context setting constraints of all other entries in the Body of Knowledge. The latter encompass the philosophical and mathematical support for GIScience as well as data models, while the constituent elements include, among others, notions of scale, spatial data quality, and openness. This knowledge area is also the place to look for the origins and future of GIScience.

UNDERSTANDING OF DATUMS, COORDINATE SYSTEMS, AND PROJECTIONS

KEY CONCEPTS AND TERMINOLOGY

  • Georeferencing – associating a map (such as a pdf without spatial information) or image (such as an aerial image without spatial information) with spatial locations.
  • Control points – consisting of multiple points, points come in pairs that match the spatial location with a point on an unreferenced image or map.
  • Spatial reference system (SRS) or coordinate reference system (CRS) – a coordinate-based local, regional, or global system used to locate geographical entities.
  • International Terrestrial Reference System (ITRS) – It is a three-dimensional coordinate system with a well-defined origin (the center of mass of the Earth) and three orthogonal coordinate axes (X,Y,Z)
  • Map projection – transforming coordinates from a curved earth to a flat map.
  • Horizontal datum – model of the earth as a spheroid (2 components, reference ellipsoid and a set of survey points both the shape of the spheroid and its position relative to the earth)
  • Vertical datum – reference point for elevations of surfaces and features on the Earth - could be based on tidal, seas levels, gravimetric, based on a geoid.
  • NAVD88 – gravity based geodetic datum in North America
  • Geodetic datum – set of control points whose geometric relationships are known, either through measurement or calculation.
  • WGS 84 – World Geodetic System - reference coordinate system used by the Global Positioning System (GPS)
  • SRID integer – spatial reference system id numbers, including EPSG codes defined by the International Association of Oil and Gas Producers
  • 4 distortions – Distance - Direction - Shape – Area
  • Mercator Projection – Preserves shape and direction, area gets distorted - projecting earth onto a cylinder tangent to a meridian.
  • Azimuthal Equidistant – planar (tangent) - used for air route distances - distances measured from the center are true - distortion of other properties increases away from the center point.
  • Cylindrical equal-area projections – preserves area, shape and distance gets distorted near the upper and lower regions of the map - straight meridians and parallels - meridians are equally spaced and the parallels are unequally spaced.
  • Conic projections – preserves directions and areas in limited areas - distorts distances and scale except along standard parallels - generated by projecting a spherical surface onto a cone.
  • Choosing a projection:
    • Latitude: Low-latitude areas (near equator) use a conical projection; Polar regions use an Azimuthal planar projection
    • Extent: Broad in East-West (e.g., the US) use a conical projection; Broad in North-South (e.g., Africa) use a transverse-case cylindrical projection.
    • Thematic: If you are doing an analysis that compares different values in different locations, typically an equal-area projection will be used.

SAMPLE QUESTION

What does georeferencing involve in the context of spatial data?

A) Associating a map (such as a PDF without spatial information) or image (such as an aerial image without spatial  information) with spatial locations. 

B) Calculating the area of a geographic feature. 

C) Determining the elevation of a point on the Earth’s surface. 

D) Converting coordinates from a flat map to a curved Earth.

Answer: A) Associating a map (such as a PDF without spatial information) or image (such as an aerial image without spatial  information) with spatial locations.

Explanation: Georeferencing is the process of linking spatial data (such as maps or images) to specific geographic locations. It allows  us to relate features on a map or image to their real-world positions on the Earth’s surface2.

UNDERSTANDING OF REPRESENTATION OF DISCRETE FEATURES AND CONTINUOUS PHENOMENA IN GIS

KEY CONCEPTS AND TERMINOLOGY

  • Discrete features – a feature that has a definable boundary, begins, and ends, for example a highway or lake.
  • Continuous phenomena – each location is a measure of something, for example elevation.
    • Measure of concentration level
    • Measure of a value in terms of a fixed point (like elevation in terms of sea level)
  • Be able to indicate if a geographic feature is either discrete or continuous.

SAMPLE QUESTION

Which of the following statements accurately describes the distinction between discrete features and continuous phenomena in  GIS?

A) Discrete features have well-defined boundaries, while continuous phenomena lack clear boundaries.

B) Discrete features are represented using continuous color scales, while continuous phenomena use distinct colors or symbols.

C) Discrete features are typically represented as points, lines, or areas, while continuous phenomena are represented as polygons.

D) Continuous phenomena are mainly nouns, whereas discrete features are derived from fixed registration points.

Answer: A) Discrete features have well-defined boundaries, while continuous phenomena lack clear boundaries.

Explanation: Discrete features refer to objects with definite boundaries, such as roads, buildings, and land parcels. These features are easily represented as points, lines, or areas on maps.

Continuous phenomena, on the other hand, lack well-defined or relevant boundaries. Examples include temperature, air quality, and  elevation. Continuous data is often represented using gradients or continuous color scales to visualize patterns across a range of  values 12.

Understanding this distinction is crucial for effective GIS data management and analysis!

KNOWLEDGE OF EARTH GEOMETRY AND ITS APPROXIMATIONS

KEY CONCEPTS AND TERMINOLOGY

  • GeoidGeoid is the shape that the surface of the oceans would take under the influence of Earth's gravitation and rotation alone, in the absence of other influences such as winds and tides - used to reference heights, by registering ocean’s water level at coastal places using tide gauges - this is how the mean sea level is determined.
  • Reference ellipsoid is a mathematically defined surface that approximates the geoid, the truer figure of the Earth, or other planetary body.
  • Oblate ellipsoid- fits the geoid to a first order approximation - formed when an ellipse is rotated about its minor axis.
  • Sphere - As can be seen from the dimensions of the Earth ellipsoid, the semi-major axis a, and the semi-minor axis b differ only by a bit more than 21 kilometers.
  • First (direct) geodetic problem - Given a point (in terms of its coordinates) and the direction (azimuth) and distance from that point to a second point, determine (the coordinates of) that second point.
  • Second (inverse) geodetic problem - Given two points, determine the azimuth and length of the line (straight line, arc or geodesic) that connects them.
  • For more information on datums, see Section 101

SAMPLE QUESTION

Which of the following statements accurately describes the difference between geoid, reference ellipsoid, and oblate ellipsoid in GIS?

A) The geoid represents the true physical shape of the Earth while the reference ellipsoid is a mathematical idealized representation of the Earth as an ellipsoid.

B) The reference ellipsoid represents the shape of the oceans under the influence of Earth’s gravity and rotation alone, while the oblate ellipsoid is formed by rotating an ellipse about its minor axis.

C) The geoid is used to reference heights by registering ocean water levels at coastal places using tide gauges, while the reference ellipsoid is associated with land use and soils data.

D) The oblate ellipsoid is primarily used for elevation modeling, while the geoid is related to land ownership and zoning.

Answer: A) The geoid represents the true physical shape of the Earth while the reference ellipsoid is a mathematical idealized representation of the Earth as an ellipsoid. What Is Geoid In Surveying? Geoid vs Ellipsoid Comparison - Civil Stuff.

KNOWLEDGE OF BASIC GEOMATICS AND RELATIONSHIPS TO GIS

According to the ISO/TC 211 series of standards, geomatics is the discipline concerned with the collection, distribution, storage, analysis, processing, and presentation of geographic data or geographic information.

In simpler terms, it involves products, services, and tools related to the integration and management of geographic (geospatial) data. Geomatics integrates science and technology from both new and traditional disciplines:

  • Geodesy: Precise measurement and understanding of Earth’s shape, gravity field, and rotation.
  • Surveying: Land, cadastral, aerial, mining, and engineering surveying.
  • Remote Sensing: Collecting data from a distance (e.g., satellite imagery, LiDAR).
  • Cartography: Creating maps and spatial representations.
  • Geographic Information Systems (GIS): Digital tools for analyzing and visualizing geographic data.
  • Global Navigation Satellite Systems (GPS, GLONASS, Galileo, BeiDou): Positioning and navigation technology.
  • Hydrography: Mapping water bodies and their features.
  • Geophysics: Studying Earth’s physical properties.
  • Navigation and Location-based Services

Geomatics plays a crucial role in understanding Earth and its phenomena. It enables us to explore geographic features, analyze spatial relationships, and make informed decisions. Whether it’s monitoring environmental changes, creating accurate maps, or managing infrastructure, geomatics is at the heart of spatial data science.

KEY CONCEPTS AND TERMINOLOGY

  • Geomatics – science and technology of gathering, analyzing, interpreting, distributing, and using geographic information (includes surveying, mapping, remote sensing, GIS, GPS)
  • Geodesy – is the science of measuring and representing the geometry, gravity, and spatial orientation of the earth in temporally varying 3D. It is called planetary geodesy when studying other astronomical bodies such as planets or circumplanetary systems.
  • Global Positioning System (GPS) – For more information on GPS, see the Section on GPS

SAMPLE QUESTION

Which of the following statements accurately describes the discipline of geomatics and its relationship to Geographic Information Systems (GIS)?

A) Geomatics involves collecting, managing, and analyzing data about Earth and its phenomena, while GIS specifically focuses on spatial data exploration.

B) Geomatics is primarily concerned with remote sensing and photogrammetry, while GIS deals with surveying and mapping.

C) Geomatics encompasses the study of land use and soils data, while GIS is limited to spatial data modeling.

D) Geomatics refers to the study of graphic representation techniques, while GIS focuses on metadata management.

Answer: A) Geomatics involves a wide range of methods and technologies for collecting, managing, and analyzing data about Earth and the phenomena arranged on and near its surface. An important component of Geomatics is Geographic Information Systems (GIS); GIS uses spatial data to explore geographic phenomena12.