Geodesy & Map Projections Flashcards

What is the approximate inverse flattening (1/f) of the WGS 84 ellipsoid?

Answer: 298.257

WGS 84 defines 1/f = 298.257223563, nearly identical to GRS 80.

Under NSRS modernization, which new datum will replace NAVD 88?

Answer: NAPGD2022

NAPGD2022 (North American-Pacific Geopotential Datum) replaces NAVD 88, while NATRF2022 replaces NAD 83.

Which projection is generally used for State Plane zones that extend mainly north-south?

Answer: Transverse Mercator

Transverse Mercator keeps scale error low along a central meridian, which suits north-south zones.

Geodetic latitude is defined as the angle between the equatorial plane and which line?

Answer: The ellipsoid normal at the point

Geodetic latitude uses the ellipsoid normal, geocentric latitude uses the radius vector, and astronomic latitude uses the plumb line.

In an Earth-Centered, Earth-Fixed (ECEF) Cartesian system, the X-axis points toward which location?

Answer: The intersection of the equator and the prime meridian

In ECEF, X points to 0 degrees latitude and 0 degrees longitude, Z points to the reference pole, and Y completes a right-handed system.

About how much ground distance does one arc-second of latitude cover?

Answer: About 30.9 m

One degree of latitude is about 111 km, so one arc-second is about 111,000 / 3,600, or roughly 30.9 m.

In a UTM zone, where is the projection scale factor exactly 1.0000?

Answer: Along two lines about 180 km east and west of the central meridian

The secant cylinder cuts the ellipsoid along two lines about 180 km either side of the central meridian, where scale is exact.