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DGCA Air Navigation · 30 questions

Map Projections: DGCA Air Navigation Questions and Answers

30 practice questions on Map Projections with answers and explanations, plus the key concepts and formulas, from the TrueHeading question bank.

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About this topic

Use this page to revise Map Projections for the DGCA Air Navigation paper. Below are the key ideas first, then 12 practice questions with answers and explanations, picked from the 30 questions in the TrueHeading bank for this topic.

In short: A cylindrical, conformal (orthomorphic) projection.

Open the full set in the student zone to answer every question, track your accuracy and take timed mock tests.

Key concepts: Map Projections

6 ideas to know cold.

Properties of the Mercator projection?

A cylindrical, conformal (orthomorphic) projection.

  • Meridians are equally spaced parallel straight lines
  • Parallels are straight and spaced further apart towards the poles
  • Rhumb lines are straight; great circles curve towards the equator-side (convex to the pole)
  • The poles cannot be shown; scale grows with latitude

Why is the Lambert conformal conic popular for aeronautical charts?

Great circles are nearly straight lines and scale is almost constant across the chart.

n=sin⁡ϕ0n=\sin\phi_0
  • Two standard parallels where scale is exact
  • Scale is contracted between them and expanded outside
  • Meridians are straight lines that converge; parallels are arcs of circles
  • Convergence factor (constant of the cone) ≈ sin of the parallel of origin

What does “conformal” (orthomorphic) mean?

Angles are preserved. Scale is the same in every direction at a point, and meridians and parallels cross at right angles.

Tip: Needed so that bearings measured on the chart are correct.

Which projection do you use near the poles?

A polar stereographic projection (azimuthal and conformal).

  • Great circles through the centre are straight lines
  • Meridians radiate from the pole as straight lines

What are the properties of a Mercator chart?

A cylindrical, conformal projection. Rhumb lines are straight lines.

Scaleϕ=Scale0cos⁡ϕ\text{Scale}_\phi=\dfrac{\text{Scale}_0}{\cos\phi}
  • Meridians parallel, parallels parallel and unequal spacing
  • Scale expands as 1/cos(latitude)
  • Great circles curve towards the equator
  • Not usable near the poles

What are the properties of a Lambert conformal conic chart?

A conic, conformal projection with two standard parallels.

Convergence=Δλ×n,n=sin⁡ϕ0\text{Convergence}=\Delta\lambda\times n,\quad n=\sin\phi_0
  • Great circles are almost straight lines
  • Convergence factor (n) = sin of the parallel of origin
  • Scale is correct at the standard parallels and slightly small between them
  • Used for aeronautical charts of mid-latitudes

Practice questions: Map Projections

Tap “Show answer” after you have tried each one.

Q1On a Mercator chart, the scale:

  1. Varies as 1/2 cosine of the co-latitude
  2. Varies as the sine of the latitude
  3. Is constant throughout the chart
  4. Varies as 1/cosine of latitude (1/cosine= secant)
Show answer

Answer: D. Varies as 1/cosine of latitude (1/cosine= secant)

Q2On a Direct Mercator chart, meridians are:

  1. Parallel, equally spaced, vertical straight lines
  2. Inclined, equally spaced, straight lines that meet at the nearer pole
  3. Parallel, unequally spaced, vertical straight lines
  4. Inclined, unequally spaced, curved lines that meet at the nearer pole
Show answer

Answer: C. Parallel, unequally spaced, vertical straight lines

Q3A direct Mercator graticule is based on a projection that is:

  1. Concentric
  2. Conical
  3. Spherical
  4. Cylindrical
Show answer

Answer: D. Cylindrical

Q4On a Direct Mercator chart a great circle will be represented by a:

  1. Curve concave to the equator
  2. Complex curve
  3. Curve convex to the equator
  4. Straight line
Show answer

Answer: A. Curve concave to the equator

Q5On a Lambert conformal conic chart, with two standard parallels, the quoted scale is correct:

  1. In the area between the standard parallels
  2. Along the two standard parallels
  3. Along the parallel of origin
  4. Along the prime meridian
Show answer

Answer: B. Along the two standard parallels

Q6On a Lambert Conformal Conic chart earth convergency is most accurately represented at the:

  1. Parallel of origin
  2. North and south limits of the chart
  3. Standard parallels
  4. Equator
Show answer

Answer: A. Parallel of origin

Q7Parallels of latitude, except the equator, are:

  1. Rhumb lines
  2. Great circles
  3. Both Rhumb lines and Great circles
  4. Are neither Rhumb lines nor Great circles
Show answer

Answer: A. Rhumb lines

Q8A straight line on a Lambert Conformal Projection chart for normal flight planning purposes:

  1. Is approximately a Great Circle
  2. Is a Loxodromic line
  3. Is a Rhumb line
  4. Can only be a parallel of latitude
Show answer

Answer: A. Is approximately a Great Circle

Q9On a transverse Mercator chart, the scale is exactly correct along the:

  1. Prime meridian and the equator
  2. Equator and parallel of origin
  3. Meridian of tangency and the parallel of latitude perpendicular to it
  4. Meridians of tangency
Show answer

Answer: D. Meridians of tangency

Q10The chart that is generally used for navigation in polar areas is based on a:

  1. Direct Mercator projection
  2. Stereographical projection
  3. Gnomonic projection
  4. Lambert conformal projection
Show answer

Answer: B. Stereographical projection

Q11On a Mercator chart a great circle appears as a curve that is:

  1. A straight line
  2. Convex towards the nearer pole
  3. A parallel of latitude
  4. Concave towards the nearer pole
Show answer

Answer: B. Convex towards the nearer pole

Q12The constant of the cone on a Lambert conformal conic chart equals:

  1. The tangent of the parallel of origin
  2. The cosine of the parallel of origin
  3. One
  4. The sine of the parallel of origin
Show answer

Answer: D. The sine of the parallel of origin

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