Chart Projections

Question 1

What is orthomorphism? What is required for it?

Answer 1

Correct bearings, and therefore shapes are also correct.

Scale about a point must be the same in all directions for a short distance
Meridians and parallels must intersect at 90*

Question 2

What is conformality?

Answer 2

It is the same as orthomorphism

Question 3

What is equivalence? What is required for it?

Answer 3

The map is equal area, or at a reduced scale.

Scale cannot be kept constant
Expansion in one scale must be equal and opposite in the other direction

Question 4

How can a scale be expressed?

Answer 4

Simple statement
Representative fraction
Graphic/ graduated scale

Question 5

What are the properties of a Mercator? (7)

Answer 5

• Meridians are parallel, evenly spaced straight lines
• Parallels are straight lines that expand away from the equator, intersect at 90*
• Scale correct at the equator, expands as sec(latitude)
• Higher than 70* latitude scale becomes too distorted
• Rhumb line is a straight line
• Great circle is a curve, concave to the equator
• It is orthomorphic

Question 6

How does scale vary on a conic projection with two standard parallels?

Answer 6

Contracts between them and expands beyond them

Question 7

What are the properties of a Lambert’s conformal?

Answer 7

• Meridians are straight lines radiating from the pole
• Parallels are concentric arcs that intersect at 90*
• Scale is correct at the 2 standard parallels
• Scale error is small so it can be considered constant on a single sheet
• Great circle is approximated by a straight line and is always closer to the pole
• Rhumb line is a curve, concave to the pole
• The map is conformal
• Adjacent sheets will fit if they have the same standard parallels

Question 8

What uses does the Lambert conformal have?

Answer 8

Radio navigation

Countries with large East - West extent

Question 9

What uses does the Mercator have?

Answer 9

Tropical maps
Dead reckoning/ celestial
Countries with large North - South Extent (transverse Mercator)

Question 10

What is the equation for determining scale?

Answer 10

Scale = Chart Distance/Earth Distance

Question 11

What are the conversions for different units of measurements

Answer 11

2.54cm = 1in
12in = 1ft
1nm = 6076ft / 1852m
1sm = 5280ft
1km = 3280ft

Question 12

What requirements should an aviation chart have?

Answer 12

• Orthomorphism (primary)
• Rhumb lines are straight lines
• Distances are measurable
• Adjacent sheets should fit

Question 13

What requirements does an aviation Map have?

Answer 13

• Shapes shown fairly correctly
• Scale fairly constant and any error distributed evenly
• Adjacent sheets fit

Question 14

What is the equation for chart convergency?

Answer 14

-CHLONG * Sin(mean Latitude)