4. Positioning Flashcards
What is latitude?
“Latitude is the angular distance from the equator to a point measured northwards or southwards along the meridian through that point”
The Parallels of Latitude circle the Earth and are expressed in degrees north or south of the equator, up to a maximum of 90°
What is longitude?
The vertical lines are called Lines of Longitude. (Meridians)
“Longitude is the shorter angular distance along the equator between the prime meridian and the meridian through that point”
They are expressed in degrees east or west of a reference known as the Prime Meridian up to a maximum of 180°
What is WGS84?
The World Geodetic System.
Essentially it relates a position above the centre of
the earth, rather than in relation to the surface, but
when combined with terrestrial data is very accurate.
It is currently the reference system being used by the
Global Positioning System (GPS), which orbit the
WGS84 datum.
It is geocentric (based on the centre of the earth)
Globally consistent within ±1 m.
What is a graticule ?
A common example of a graticule
is a grid of lines on a map which corresponds to longitude and latitude.
A graticule is a network of lines which can be used for geographic plotting, scale, and focusing, depending on the application.
How far does 1 of Longitude at the Equator subtend?
60nm
How far does 1 of Longitude at 60° subtend
30nm
On a map, the terms ‘quarter million’, ‘half million’ and ‘million’ refer to?
The ratio between the chart distance and the Earth distance that it represents is the Chart Scale
What is the angular difference between an aircraft’s heading and its track called ?
Drift Angle
What do the symbols when shown on a 1:500,000 chart, indicate?
The ratio between the chart distance and the Earth distance that it represents is the Chart Scale
How is the scale represented on a map or chart? (3)
- a fraction or a ratio
- statement in words
- a graduated scale
NOTE: Scale = Chart Distance divided by Earth Distance
What are the OS references using the National Grid?
Grid Reference
they can be:
- 4 figure (accurate to 1000 meters)
- 6 figure (accurate to 100 meters)
- 8 figure (accurate to 10 meter)
- 10 figure (accurate to 1 meter) used by GPS
Remember Eastings first followed by Northings i.e., “along the passage and up the stairs”
What OS Maps are used for?
Combined civil and military Search and Rescue services over land (e.g., mountain search and rescue) Airfield Crash Maps which are made available to: Fire, Ambulance & Police.
Enabling the controller to give the precise position of an accident.
