GEOG215 Flashcards
GIS
Geographic Information System. System for capturing, storing, manipulating, and displaying data that is systematically related to the Earth.
What ways can GIS be used?
We can investigate patterns within a location, geographic relationships, model what-if scenarios, and store large data sets.
What are the stages of a GIS project?
Data Input (GPS collection, UAV) –> Data Storage –> Data Manipulation (align with coordinate system) –> Data Analysis (slope) –> Data Output (3D model).
What do spatial professionals do?
Capture, analysis, modelling, design, and visualization of geographic data to deliver insights and understanding.
What is GI Science?
Science behind the technology. A scientific approach to the fundamental issues arising from the use of GIS and related technologies
What is geographic information?
Any information that refers to a location on the Earth’s surface. So, = spatial data.
What is spatial data?
Spatial data is data that has both:
- Description
- Spatial component (geometry)
Eg, where the city is located and what it is beside.
Data Model
A spatial database is a realisation of a data model.
- Real world view
- Map/screen view (simplification of real world to give spatial component)
What are layers?
The visual representation of an individual geographic dataset in any digital map environment. Works similar to a legend item on a paper map within the same location.
Why do we need layers?
To represent real world data of the same location without complicating display/storage.
Why is representing things in layers so useful?
Layers can be turned on and off, allowing for the representation of specific data alone or in conjunction.
What are the two types of spatial data?
Vector and Raster
Spatial Data: Vector
Spatial or coordinate data represents features that have a known location on the earth. Comprises:
- Points (X and Y locations)
- Line (Connected X and Y locations)
- Polygon (Connected X and Y locations that contain information in a enclosed area).
Vector: Points
X and Y locations
Vector: Lines
Connected X and Y locations
Vector: Polygon
Connected X and Y locations that contain information in a enclosed area
Spatial Data: Raster
Row and column matrix which represents geographic space. Includes aerial imagery.
Raster cannot identify that the cell next to it contains information that is similar or different - making it harder when representing roads, wetlands, etc.
Geometric Representation of Spatial Feature
Uses geometries of point, polyline, and polygon to represent vector-base spatial features.
Points = 1 or more point.
Polyline = set of line segments (one or more lines, connected or unconnected).
Polygon = 1 or more areas.
Vector vs Raster Data
Vector: object based - it’s all about the spatial features. Each feature is coded uniquely, which allows overlap - raster data cannot.
Raster: Geographical features are represented by values in matrix (or mesh/lattice grid/array). Elevation is a surface, where each cell has a value.
Attribute Data
Information linked to the geographic features (spatial data) that describe features. They are the “non-graphic information associated with a point, line, or area elements in a GIS.”
Vector data offers much more attribute data, while raster is much less detailed.
What 3D models have been used to approximate the Earth’s surface?
Ellipsoid, geoid, spheroid.
Why can’t we use a sphere for coordinate systems?
Earth bulges at the equator, doesn’t account for topography.
What are geographic coordinates measured in?
Lat and long, degrees, minutes, seconds.
What is a meridian?
Lines of equal longitude, beginning in Greenwich. Measures 180, East to West.
What is a parallel?
Lines of equal latitude, North to South
What is WGS84?
Datum, based on observations of TRANSIT satellite system (1-2m accuracy). Developed for US Defence. Improved with GPS data WGS84 (G1150). Based on ellipsoid earth model.
What are Cartesian coordinates?
Based on X, Y and Z axes. Axes do not have to be perpendicular. Can calculate distance by coordinate geometry but not attached to real world.
Good over small areas of the earth where curvature isn’t influential.
Why do we need to convert from one coordinate system to another?
Ensure data is aligned and can work together, regardless if data from different sets are in different forms.
Datum
A mathematical model of the earth where an origin and surface are defined. In abstract, they are errorless (every point has a unique and accurate coordinate).
Projection
Representation, on a plan surface, of the meridians of longitude and parallels of latitude, reference to which defines any point on the earth surface.
By picking a particular projection system, we move from geodesic to 2D. This information is stretched and distorted. Over small areas, this is less problematic.
What methods of projections are there?
Planar (Most often touches globe at a single point, trade routes)
Cylindrical (Flat piece of paper wrapped around the globe, Distortion is lowest at the equator and highest at the poles)
Conical (Touches globe at a line of parallel. Cannot be used for world map. Good for countries).
What is an EPSG?
Public registry/reference system of datums
What are qualities a projection can have?
Equal area, true shape, true scale
Name the common types of projection?
Transverse Mercator: conformal, used for global projections, is transverse because the central meridian is at right angles to the equator.
Lambert Conformal Conic: Used for mapping east/west stretches at mid-latitudes. Conical.
Albers Equal Area Conical: Similar to lambert but is equal area
What is a datum transformation?
Change from one datum (3D view) to another datum (3D view).
What is georeferencing?
Also known as registering. Control points needed (I know where this point is in both areas), along with warping to create accuracy between real data and imagery.
How do coordinate systems and projections fit together?
You have to have an orange before you can peel. You have to have a 3D view before you can project it into a 2D system.
NZ Transverse Mercator (2000)
Most used in NZ, based on NZGD2000 Datum. Locally assumed North only true at one meridian - because lines have to curve to meet poles, and only one line will directly hit North.
TM useful for long, narrow countries.
NZ Map Grid (1949)
Was replaced by NZTM, planar surface, has an origin, well-defined, based on NZGD49, static (no change to land). Distortion is larger over distances. Does not transfer over to global projections well.
Centre of projection is the centre of NZ, so further from the centre, more distortion there is.
What is Raster Data?
Row and column matrix which represents geographic space.
What is Vector Data?
Spatial or coordinate data represents features that have a known location on the earth, including points, lines, and polygons.
What are Attribute Tables?
Information linked to the geographic features (spatial data) that describe features. They are displayed as rows and columns.
What are Rows also called?
Rows (Record/Tuple)
What are Columns also called?
Columns (Field/Item)
Can Raster and Vector be used for the same data?
Some dataset will be better suited to one representation, although you can technically use either (one will be harder).
What is Metadata?
Data about data, like a label on a tin. It is data about the WHOLE layer, not just one data point.