PS PS Map Projections & Cartography 1 — Questions and Answers
Question 1: What type of map projection preserves the shape of small areas but distorts area over large regions?
- Conformal projection (Correct answer)
- Equal-area projection
- Equidistant projection
- Azimuthal projection
Correct answer: Conformal projection
Conformal projections preserve local angles and shapes, but they distort area as distance from the central meridian increases.
Question 2: The State Plane Coordinate System (SPCS) uses which two map projections depending on the orientation of the state?
- Lambert Conformal Conic and Transverse Mercator (Correct answer)
- Albers Equal-Area and Mercator
- Stereographic and Gnomonic
- Polyconic and Azimuthal Equidistant
Correct answer: Lambert Conformal Conic and Transverse Mercator
SPCS uses the Lambert Conformal Conic for east-west-oriented states and the Transverse Mercator for north-south-oriented states.
Question 3: What is the scale factor at the central meridian of a Transverse Mercator projection used in the State Plane Coordinate System?
- Less than 1.0000 (Correct answer)
- Exactly 1.0000
- Greater than 1.0000
- Variable depending on latitude
Correct answer: Less than 1.0000
In SPCS Transverse Mercator zones, the scale factor at the central meridian is set slightly less than 1 (e.g., 0.9999) so that the projection surface secants the ellipsoid, reducing maximum distortion.
Question 4: Which datum and ellipsoid are used as the basis for the current North American State Plane Coordinate System (SPCS 83)?
- NAD 83 / GRS 80 ellipsoid (Correct answer)
- NAD 27 / Clarke 1866 ellipsoid
- WGS 84 / WGS 84 ellipsoid
- NAVD 88 / GRS 80 ellipsoid
Correct answer: NAD 83 / GRS 80 ellipsoid
SPCS 83 is referenced to NAD 83, which uses the GRS 80 ellipsoid as its geometric foundation.
Question 5: What is the purpose of a 'grid factor' (combined scale factor) in State Plane coordinate computations?
- To convert ground distances to grid distances (Correct answer)
- To convert latitudes to northings
- To transform NAD 27 to NAD 83 coordinates
- To calculate true north from grid north
Correct answer: To convert ground distances to grid distances
The combined (grid) scale factor is multiplied by a ground distance to produce the corresponding grid distance on the State Plane projection.
Question 6: On a topographic map with a 1:24,000 scale, what does a map distance of 1 inch represent on the ground?
- 2,000 feet (Correct answer)
- 24,000 inches
- 1 mile
- 24,000 feet
Correct answer: 2,000 feet
At 1:24,000, one map inch equals 24,000 ground inches; dividing by 12 gives 2,000 feet.
PS PS Map Projections & Cartography 1
What type of map projection preserves the shape of small areas but distorts area over large regions?