GIS Map Projections and Datums 2 — Questions and Answers
Question 1: Which map projection is used as the basis for the Universal Transverse Mercator (UTM) coordinate system?
- Lambert Conformal Conic
- Albers Equal-Area Conic
- Transverse Mercator (Correct answer)
- Azimuthal Equidistant
Correct answer: Transverse Mercator
UTM is based on the Transverse Mercator projection, applied in 60 narrow north-south zones to minimize distortion.
Question 2: What does a 'false easting' value accomplish in a projected coordinate system?
- It rotates the coordinate grid to align with magnetic north
- It shifts the origin eastward to keep all X coordinates positive (Correct answer)
- It scales coordinates to match sea-level elevations
- It converts geographic coordinates to radians
Correct answer: It shifts the origin eastward to keep all X coordinates positive
A false easting offsets the X-axis origin so that all easting values within the zone are positive, avoiding negative coordinates.
Question 3: The Mollweide projection preserves which property?
- Shape (conformal)
- Distance from center point
- Equal area (Correct answer)
- True compass bearings
Correct answer: Equal area
Mollweide is a pseudocylindrical equal-area projection often used for world maps showing global distributions.
Question 4: Which datum is used by the GPS satellite system as its native reference frame?
- NAD27
- NAD83
- WGS84 (Correct answer)
- ITRF2014
Correct answer: WGS84
GPS satellites broadcast positions referenced to WGS84, the World Geodetic System of 1984.
Question 5: A map projection that correctly represents the shape of small areas but distorts size is called:
- Equal-area
- Conformal (Correct answer)
- Equidistant
- Azimuthal
Correct answer: Conformal
Conformal (orthomorphic) projections preserve local angles and shapes but distort areas, especially far from the standard line.
Question 6: The standard parallel of a conic projection is the latitude where:
- Distortion is at its maximum
- The cone intersects or is tangent to the globe (Correct answer)
- The prime meridian is defined
- Scale factor equals zero
Correct answer: The cone intersects or is tangent to the globe
At the standard parallel, the cone touches (tangent) or intersects (secant) the ellipsoid, producing zero scale distortion along that line.
Question 7: Converting coordinates from NAD27 to NAD83 typically requires a datum transformation because:
- The two datums use different prime meridians
- They define the Earth's shape using different ellipsoids and origins (Correct answer)
- NAD83 uses feet while NAD27 uses meters
- They are based on different map projections
Correct answer: They define the Earth's shape using different ellipsoids and origins
NAD27 uses the Clarke 1866 ellipsoid with a Kansas origin, while NAD83 uses GRS80 with an Earth-centered origin, causing positional offsets up to 100 meters.
GIS Map Projections and Datums 2
Which map projection is used as the basis for the Universal Transverse Mercator (UTM) coordinate system?