Charts and Projections (Nav) Flashcards
What are the three things we want from a map or chart?
Constant angles, i.e. the relationships between angles do not change from one place to another on the chart.
Constant shapes, i.e. things look the same shape they are.
Constant scale, i.e. things which are X distance from each other on one part of the map are the same distance apart in reality as two things which are X distance apart in a different part of the map.
What are the three categories of chart projection?
Azimuthal, which centered over a pole. Great for angles staying true, otherwise, not a lot of use.
Cylindrical, which is centered at the equator. Good for having a general idea of the whole world at once, but very distorting towards the poles.
Conical (sometimes called Lambert Conical), which centers on an arbitrary line of latitude created by placing an imaginary cone over the globe, and using the points of contact it makes as this latitude. Most commonly used in aviation.
What are the two sub-types of conical projections, and what are their advantages and disadvantages?
There’s the sort where the map is “true” in the middle, i.e. the “cone” over the “globe” touches it in one line, or the sort where the map is “true” along two lines, 1/3 up and down the page respectively. This is achieved by projecting the imaginary cone through the surface of the globe, causing it to intersect in two diverging lines.
The second sort is generally preferred, as overall, the map is closer to reality, however in the first sort, the middle of the map is the most accurate part, unlike the second, and therefore this may be preferred if creating a custom map for a particular use, where the highest-accuracy section can be placed over the bit you particularly care about.
How do great circles and Rhumb lines appear on the different projections? How about lines of latitude and longitude?
On a conical projection, latitudinal and longitudinal lines will converge and diverge towards the pole/equator end of the map, respectively. Rhumb lines will curve towards the equator, and great circles will appear as straight lines, i.e. orthodromes.
On a cylindrical projection, the lines of latitude are straight, but lines of longitude converge towards the poles. Rhumb lines will appear straight, and orthodromes will converge towards the poles.
Azimuthal projections are strange and not worth worrying about, but basically work like extreme conical projections.
What properties does Lambert’s Conical Projection have?
Great Circle lines are straight, Rhumb lines curve towards the equator. Technically not true scale, but close enough for practical purposes. Angles are true, and shape distortion is only very slight.
What are the standard scales for en-route and nav charts?
1:1,000,000 and 1:500,000, respectively.
What is a positional approach terrain chart, and why might one exist?
A chart showing you the ways you can approach a landing site with difficult or obstructive terrain around it, for example mountains or buildings.
What are SIDs and STARs?
Standard Instrument Departure charts and Standard Arrival charts.
What are the two types of aerodrome charts?
Regular ones, as produced for AIPs, and visual specific aerodrome charts, for VFR pilots.
What tasks must a chart allow a pilot to accomplish? 4 answers.
Navigation
Avoidance of obstacles
Avoid restricted airspace
Use flight paths according to airspace structure
