GIS Map Projections and Datums 4

Question 1

Which projection property is preserved by the Azimuthal Equidistant projection from its center point?

Accepted Answer

True scale (distance) along all radii from the center

Answer

The Azimuthal Equidistant projection preserves true distances and directions from the central point to all other points on the map.

Question 2

A GIS analyst notices a 30-meter discrepancy between GPS points and legacy survey data. The most likely cause is:

Accepted Answer

A datum mismatch between WGS84 and NAD27

Answer

Horizontal offsets of 20–100 meters between WGS84/NAD83 and NAD27 are common in the contiguous US, the most frequent source of such discrepancies.

Question 3

The Albers Equal-Area Conic projection is most appropriate for mapping:

Accepted Answer

East-west extents in mid-latitudes such as the conterminous United States

Answer

Albers is optimized for regions with greater east-west than north-south extent at mid-latitudes, making it ideal for CONUS maps.

Question 4

What is the geoid, and how does it relate to a geodetic datum?

Accepted Answer

The geoid is an equipotential surface approximating mean sea level; datums use an ellipsoid that best fits it

Answer

The geoid is an irregular equipotential surface (mean sea level); geodetic datums use a mathematical ellipsoid fitted to approximate the geoid for horizontal positioning.

Question 5

On a Mercator projection, rhumb lines appear as:

Accepted Answer

Straight lines

Answer

Mercator preserves angles (conformal), so a course of constant compass bearing (rhumb line) plots as a straight line, which is why it is valued for nautical navigation.

GIS - Geographic Information System Practice Test

GIS - Geographic Information System Practice Test

GIS Map Projections and Datums 4