GIS Geospatial Data Fundamentals 5 — Questions and Answers
Question 1: What is the key difference between a geographic coordinate system and a projected coordinate system?
- Only projected systems can store elevation data
- A geographic system uses a 3D ellipsoid reference; a projected system flattens it onto a 2D plane (Correct answer)
- Geographic systems are used only for global datasets; projected systems only for local ones
- A projected system always has higher positional accuracy than a geographic system
Correct answer: A geographic system uses a 3D ellipsoid reference; a projected system flattens it onto a 2D plane
A geographic CRS references positions on a 3D ellipsoidal model of the Earth using degrees of latitude/longitude, while a projected CRS maps that surface onto a flat plane with linear units.
Question 2: Which spatial data quality dimension addresses whether all required features are present in a dataset?
- Positional accuracy
- Temporal accuracy
- Completeness (Correct answer)
- Logical consistency
Correct answer: Completeness
Completeness measures whether a dataset contains all expected features and attributes and whether any are missing or redundant.
Question 3: What does the term 'scale' represent on a reference map?
- The number of layers contained in the map document
- The ratio of a distance on the map to the corresponding distance on the Earth's surface (Correct answer)
- The coordinate system used by the map
- The resolution of the raster background image
Correct answer: The ratio of a distance on the map to the corresponding distance on the Earth's surface
Map scale expresses the relationship between map distance and real-world distance, written as a representative fraction (e.g., 1:24,000 means 1 unit on the map equals 24,000 units on the ground).
Question 4: In vector GIS, which geometry type is most appropriate for representing a city at a global map scale?
- Polygon
- Line
- Point (Correct answer)
- Multipart polygon
Correct answer: Point
At global scales, cities are too small to render as polygons and are best represented as point features, with their geographic center as the location.
Question 5: What is 'geocoding' in GIS?
- Converting raster data to vector format
- Translating a textual address into geographic coordinates (a point location) (Correct answer)
- Assigning projection information to a dataset that lacks it
- Encoding topological relationships between features
Correct answer: Translating a textual address into geographic coordinates (a point location)
Geocoding matches address strings against a reference dataset (address locator) to generate point coordinates representing each address's location.
Question 6: Which of the following best describes 'feature extraction' from remote sensing imagery?
- Downloading imagery from a satellite data provider
- Identifying and delineating specific objects or land cover classes from image data (Correct answer)
- Reprojecting imagery to match a base map layer
- Applying color enhancements to raw satellite bands
Correct answer: Identifying and delineating specific objects or land cover classes from image data
Feature extraction uses spectral, spatial, and contextual analysis to identify and map specific objects (buildings, roads, water bodies) or land cover types from imagery.
Question 7: What is the function of a 'lookup table' (or domain) in GIS attribute management?
- To store the spatial coordinates of features
- To restrict attribute field values to a predefined set of valid entries (Correct answer)
- To calculate derived fields using mathematical expressions
- To link two datasets by their geographic proximity
Correct answer: To restrict attribute field values to a predefined set of valid entries
A lookup table or coded value domain constrains what values can be entered in a field (e.g., only 'Residential', 'Commercial', or 'Industrial' for land use), reducing data entry errors.
GIS Geospatial Data Fundamentals 5
What is the key difference between a geographic coordinate system and a projected coordinate system?