lecture 3 Flashcards
(20 cards)
how can earth be conceptualised via models?
flat, spherical, ellipsoidal, and geoid
how do ellipsoidal models account for changes at the poles?
earth gets flat at poles, semi-minor and semi-major axis used.
geoid models account for gravity; what does this mean for the model?
produces equipotential surfaces (mean sea-level) and ensures consistency across continents.
example of ellipsoidal model?
WGS84
example of geoid model?
EGM96
What do datums define?
origin and orientation of coordinate systems, often based off of geoid/ellipsoidal models
what does comparing different datums recquire?
specific transformations, datum dependant
main types of map projections?
cylindrical, conic, azimuthal
what is the point of map projections?
to minimise particular distortions - they make it minimal, but there is always some distortion present
what do global X,Y,Z represent and what are they used for?
defined in terms of gravitational centre of earth of reference ellipsoid, used to convert between projections (datum) types
why is it important to know the map projection in coordinate reference frame?
ensures accurate location measurement
what are parameter transformations essential for?
accurate conversions
what does the ordnance survey provide in terms of transformations?
transformations between projections which is crucial for consistency when using multiple datasets.
what is essential for accurate analysis?
data consistency, map projection and units of measurements
what role do software tools play?
to facilitate data transformations.
what is due diligence required for?
verifying data consistency before analysis.
what is verbal representation?
it relates two different units of measurements; the first being data in GIS, second to reality. a bit like a ratio also
what is representative fraction?
the scale of a map as a ratio/fraction; ratio between the map a reality.
what happens to data volume as the scale increases?
data volume also increases
small scale data vs large scale data
small scale has large amount of generalisation from realist, whilst large scale has lower amounts.
