Nav 07 - 09 - Map Projections Flashcards
Review Questions
What is the definition of Latitude?
Angular distance from the equator measured along a Meridian
Review Questions
What is the definition of Longitude
A semi-Great Circle of the surface of the Earth joining the poles of the earth
What is a map?
A small scale, flat surface representation of some portion of the earth’s surface
Define Conformality
The correct representation of angles
For a map to be conformal, what must be met?
Meridians and parallels must intercept at right angles
Scale must be the same in all directions or change at a constant rate
Define Orthomorphism
Shapes are correctly defined
To possess correct shape, a map must be:
Conformal
Scale must be the same in all directions
True or false
It is difficult to keep the scale constant over an entire surface, but it can be considered correct over small areas.
False, it is impossible to keep the scale constant over an entire surface
Define Scale
A ratio of given distance on a map to the actual distance on the earth
What are the methods of expressing scale?
Representative fraction
Statement in words
Graduated scale
A 1 : 500 000 map is what size of scale, show what size of area, and show more of what compared to a 1 : 1 000 000 map?
A 1 : 500 000 map is a large scale, shows a smaller area and more detail than a 1 : 1 000 000 map, which show a larger area with less detail.
The three types of map projections in general use are?
Cylindrical
Conical
Azimuthal / Tangential
A Mercator projection is derived from what map projection?
Cylindrical
On a Mercator projection, a Rhumb line and a Great circle are illustrated how?
A Rhumb line is straight, a Great circle is curved and convex towards nearer pole.
Describe the following Mercator Projection properties.
Parallels Meridians Scale Shapes Great Circle Rhumb Line
Parallels: Straight lines, unequally spaced
Meridians: Straight lines, parallel, equally spaced
Scale: Correct at equator, expands away from equator
Shapes: Preserved (approx) near equator, but distorts increasingly away from equator.
Great Circle: Curved, convex to nearer pole
Rhumb Line: Straight lines
What are the limitations of the Mercator Projection map?
Excessive scale expansion
Enormous area distortion in higher latitudes
Great Circles are plotted as curved lines
What are the other cylindrical projections (apart from standard cylindrical)?
Transverse Mercator
Oblique Mercator
A Transverse Mercator map is useful for what routes?
North-South routes along a given meridian.
True or false
An Oblique Mercator map is used to show regions along a Great Circle other than the Equator or a particular meridian of longitiude.
True
What type of map is a Oblique Mercator used to create?
A strip map
Points along a strip map retain all the advantages of the Mercator at the ________.
Equator
The line of tangency on a strip map is a straight line and is a (Rhumb line or Great Circle)?
Great Circle
The Lambert Conformal projection is a variation of what projection?
Conical
How many points of tangency does a Lambert Conformal map have?
2 points of tangency
Describe the following Lambert Conformal Properties
Parallels Meridians Scale Shapes Great Circles Rhumb lines
Parallels: Concentric circles meet meridians at right angles
Meridians: Straight lines meet at the pole
Scale: Correct at two standard parallels (SP)
Between SPs: contracts
Outside SPs: Expands
Considered correct over a single sheet
Shapes: Approximately preserved everywhere
Great Circles: Approximately straight lines
Rhumb lines: Concave to nearest pole
What are some limitations of the Lambert Conformal?
Limited to use near the Standard Parallels, due to distortion that happens as you move away from SPs
Good choice for mid-latitude countries like Canada
Many charts used in RCAF are Lambert Conformal
VNC, ONC, JNC
Polar stereo maps are which type of projection?
Azimuthal
Describe the following Polar Stereo Properties
Parallels Meridians Scale Shapes Great Circles Rhumb lines
Parallels: Concentric, unequally spaced circles concave to nearest pole
Meridians: Straight lines, converging at the pole (like spokes on a bike tire)
Scale: Expands equally in all directions away from the pole
Shapes: Correct around point of tangency, distorted elsewhere
Great Circles: Approximately straight lines in polar region
Rhumb lines: Concave to nearest pole
In what latitudes are Polar Stereographic maps used? Why?
Used in high latitudes only, 45° - 90°
Below 45° there is too much distortion to be a viable tool
What are the desirable map properties?
Great Circles - Straight lines Rhumb lines - Straight lines Angles - Correct Shape - Correct Size - Correct Scale Correct and constant
The following charts have what in common?
Global Navigation and Planning Chart (GNC)
Jet Navigation Chart (JNC)
Operational Navigation Chart (ONC)
VFR Navigation Chart (VNC)
They are all used in the RCAF and are all Lambert Conformal projections (conical)
A GPH 206/ 207 are for what altitudes and are what projections? Are they used on IFR flights?
GPH 206 - Low altitude and Lambert Conformal
GPH 207 - High altitude and Lambert conformal
Used on IFR flights
Review Questions
What are the desirable map properties?
Great Circles - Straight lines Rhumb lines - Straight lines Angles - Correct Shape - Correct Size - Correct Scale Correct and constant
Review Questions
What are some plotting charts used in the RCAF?
GNC ONC JNC VNC GPH 206 / 207
