Certified Photogrammetrist Geodesy & Map Projections — Questions and Answers

Question 1: NAD 83 coordinates are referenced to which ellipsoid?

Clarke 1866
GRS 80 (Correct answer)
WGS 72
Bessel 1841

Correct answer: GRS 80

NAD 83 uses the GRS 80 ellipsoid, while NAD 27 used Clarke 1866.

Question 2: A GNSS point has ellipsoid height h = 152.40 m and geoid height N = -30.10 m. What is its orthometric height H?

182.50 m (Correct answer)
122.30 m
152.40 m
-122.30 m

Correct answer: 182.50 m

H = h - N = 152.40 - (-30.10) = 182.50 m.

Question 3: What scale factor is applied at the central meridian of every UTM zone?

1.0000
0.9999
0.9996 (Correct answer)
1.0004

Correct answer: 0.9996

UTM uses a central meridian scale factor of 0.9996 to balance distortion across the 6-degree zone.

Question 4: Which projection is typically used for State Plane zones that extend mainly east-west?

Transverse Mercator
Lambert Conformal Conic (Correct answer)
Oblique Mercator
Polyconic

Correct answer: Lambert Conformal Conic

Lambert Conformal Conic keeps scale error low along its standard parallels, which suits east-west zones.

Question 5: What is the deflection of the vertical?

The angle between the plumb line and the ellipsoid normal (Correct answer)
The angle between grid north and geodetic north
The difference between magnetic and true north
The angle between two adjacent meridians

Correct answer: The angle between the plumb line and the ellipsoid normal

Deflection of the vertical is the angle between the direction of gravity (plumb line) and the ellipsoid normal at a point.

Question 6: In a conformal projection grid, what does the convergence angle describe?

The difference between ellipsoid and orthometric heights
The scale distortion at a point
The angle between magnetic north and grid north
The angle between grid north and geodetic (true) north (Correct answer)

Correct answer: The angle between grid north and geodetic (true) north

Grid convergence is the angle between grid north and geodetic north, and it grows with distance from the central meridian.

Question 7: NAVD 88 was held fixed at a single tide-gauge benchmark located where?

Sandy Hook, New Jersey
Galveston, Texas
Father Point/Rimouski, Quebec (Correct answer)
San Francisco, California

Correct answer: Father Point/Rimouski, Quebec

NAVD 88 was a minimally constrained adjustment fixed at the Father Point/Rimouski benchmark in Quebec.

Question 8: A project site lies at longitude 105 degrees W. Which UTM zone has this longitude as its central meridian?

Zone 12
Zone 13 (Correct answer)
Zone 14
Zone 18

Correct answer: Zone 13

Zone 13 spans 108 to 102 degrees W, so its central meridian is 105 degrees W.

Question 9: What false easting is assigned to the central meridian of every UTM zone?

10,000,000 m
0 m
2,000,000 m
500,000 m (Correct answer)

Correct answer: 500,000 m

A 500,000 m false easting keeps all eastings within a zone positive.

Question 10: What false northing is applied to UTM coordinates in the Southern Hemisphere?

10,000,000 m (Correct answer)
500,000 m
0 m
1,000,000 m

Correct answer: 10,000,000 m

Southern Hemisphere UTM assigns the equator 10,000,000 m north so northings stay positive.

Question 11: Which factor converts a measured horizontal ground distance to a State Plane grid distance?

Grid convergence angle
Geoid separation alone
Combined factor (grid scale factor times elevation factor) (Correct answer)
Inverse flattening

Correct answer: Combined factor (grid scale factor times elevation factor)

Multiplying ground distance by the combined factor first reduces it to the ellipsoid and then applies projection scale.

Question 12: Which projection keeps areas true, so it is preferred for thematic land-cover maps of the conterminous United States?

Lambert Conformal Conic
Mercator
Albers Equal-Area Conic (Correct answer)
Stereographic

Correct answer: Albers Equal-Area Conic

Albers Equal-Area Conic preserves area, which is why USGS uses it for national land-cover data.

Question 13: Which current NGS hybrid geoid model converts NAD 83(2011) ellipsoid heights to NAVD 88 orthometric heights?

EGM2008
USGG2012
GEOID18 (Correct answer)
GEOID03

Correct answer: GEOID18

GEOID18 is the NGS hybrid model fitted to NAD 83(2011) GPS-on-benchmarks to yield NAVD 88 heights.

Question 14: A 7-parameter Helmert (similarity) transformation between datums consists of which parameters?

3 translations, 2 rotations, 2 scales
3 translations, 3 rotations, 1 scale (Correct answer)
4 translations, 2 rotations, 1 scale
6 translations, 1 scale

Correct answer: 3 translations, 3 rotations, 1 scale

The Helmert transformation uses three shifts, three axis rotations, and one uniform scale factor.

Certified Photogrammetrist Geodesy & Map Projections

NAD 83 coordinates are referenced to which ellipsoid?

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