GIS week 4 Flashcards
(26 cards)
What is the key difference between 2D and 3D in GIS?
2D data only uses x and y coordinates; 3D data also includes z for volume.
Why is Wolfenstein 3D not truly 3D?
It simulates 3D using 2D techniques, creating a “2.5D” effect without full 3D access.
What does a 2D geological map of the Isle of Mull show?
It shows x and y coordinates but no depth (z) information.
Why is a Digital Terrain Model (DTM) not true 3D?
It’s a surface in 3D space but mathematically 2D (x and y only).
What defines true 3D in geospatial data?
Including x, y, and z coordinates to represent volumetric data.
How are the x, y, and z axes defined in global systems?
X: Prime Meridian, Y: Equator, Z: variable by datum.
Why is the Z dimension problematic in GIS?
The Earth’s shape as an oblate spheroid makes a centre-based Z unreliable.
What is the difference between an ellipsoid and a geoid?
An ellipsoid is a simple model; a geoid is gravity-based and irregular.
What factors affect the geoid’s shape?
Lithology, tides, tectonics, water depth, and crustal heating.
What vertical reference does the UK Ordnance Survey use?
The OSGB36 datum, tied to mean sea level at Newlyn, Cornwall.
How does OS GPS differ from the OSGB36 system?
It uses ETRS89, a global WGS84-based reference.
Why are transformations between coordinate systems necessary?
Different datums produce varying x, y, z values; transformations align them.
What is a voxel in GIS?
A 3D pixel with x, y, z coordinates and attributes (e.g., density, porosity).
How are voxel layers created in ArcGIS Pro?
By using discrete or continuous data to build 3D grids.
What does a voxel model of Dutch soil profiles represent?
Discrete categories like soil types.
What does a voxel model of Gulf of Mexico temperature show?
Continuous data interpolated across a 3D space.
What defines discrete data in GIS?
Countable, categorized data with distinct boundaries.
What defines continuous data in GIS?
Smooth, variable data without clear boundaries (e.g., temperature).
How does 3D kriging work in ArcGIS Pro?
It uses Bayesian interpolation to build 3D voxel models from points.
What is the purpose of 3D visualisations in GIS?
To display and analyse volumetric data (e.g., atmosphere, ocean).
What is an isosurface in 3D data?
A surface of equal value in a 3D dataset (e.g., temperature).
Why are critical minerals important for renewable technologies?
They’re essential for batteries, wind, solar, and electric vehicles.
What are the ethical issues with cobalt mining?
Child labour, environmental damage, and health risks in places like the DRC.
What are the environmental risks of nickel mining?
Deforestation, pollution, and diseases like cancer and fibrosis.
