GIS Geospatial Data Fundamentals 3 — Questions and Answers
Question 1: What is the primary difference between geographic coordinates (latitude/longitude) and projected coordinates?
- Geographic coordinates use meters; projected coordinates use degrees
- Geographic coordinates are angular measurements on an ellipsoid; projected coordinates are linear measurements on a flat surface (Correct answer)
- Geographic coordinates are only used for raster data; projected coordinates for vector data
- Geographic coordinates are more accurate than projected coordinates
Correct answer: Geographic coordinates are angular measurements on an ellipsoid; projected coordinates are linear measurements on a flat surface
Latitude and longitude express angular positions on the curved Earth, while projected coordinates flatten the Earth onto a plane using linear units like meters.
Question 2: Which GIS operation combines attributes from two overlapping polygon layers to create a new layer containing all features from both?
- Clip
- Dissolve
- Union (Correct answer)
- Intersect
Correct answer: Union
A Union overlay preserves all features and attributes from both input layers, splitting polygons where they overlap.
Question 3: In raster data, what term describes the problem where a single cell straddles a boundary between two land cover types?
- Mixed pixel (mixed cell) (Correct answer)
- Datum shift
- Rubber sheeting
- Edge matching
Correct answer: Mixed pixel (mixed cell)
A mixed pixel occurs when a raster cell covers an area containing more than one land cover class, forcing the analyst to assign a single dominant value.
Question 4: What does 'metadata' provide in the context of a geospatial dataset?
- The actual coordinate values of each feature
- Descriptive information about the dataset including its source, date, accuracy, and projection (Correct answer)
- The symbology used to render features on a map
- The SQL queries used to filter records
Correct answer: Descriptive information about the dataset including its source, date, accuracy, and projection
Geospatial metadata (often following standards like ISO 19115 or FGDC) documents who created the data, when, how accurate it is, and what projection it uses.
Question 5: Which measurement scale allows only categorization and labeling with no implied order or mathematical relationship?
- Ratio
- Interval
- Ordinal
- Nominal (Correct answer)
Correct answer: Nominal
Nominal scale data assigns labels to categories (e.g., soil type: clay, sand, silt) without implying any ranking or numeric relationship.
Question 6: What is a Triangulated Irregular Network (TIN) primarily used for in GIS?
- Representing road networks as connected line segments
- Modeling continuous surfaces like terrain using triangular facets (Correct answer)
- Storing point cloud data from LiDAR sensors
- Classifying land use from satellite imagery
Correct answer: Modeling continuous surfaces like terrain using triangular facets
A TIN models a surface by connecting irregularly spaced sample points into non-overlapping triangles, efficiently representing terrain with varying detail.
Question 7: Which of the following best describes 'positional accuracy' in a geospatial dataset?
- The completeness of attribute records in the table
- How closely feature locations match their true positions on the Earth (Correct answer)
- The logical consistency of topology rules
- The currency (up-to-dateness) of the data
Correct answer: How closely feature locations match their true positions on the Earth
Positional accuracy measures how closely mapped feature locations correspond to their actual real-world positions, often reported as RMSE.
GIS Geospatial Data Fundamentals 3
What is the primary difference between geographic coordinates (latitude/longitude) and projected coordinates?