Week 1-3: GIS concepts Flashcards
Types of GIS q’s + e.g’s
Location. Where is the nearest shop?
Patterns. Where do high concentrations of students live?
Trends. Where are glaciers retreating in the European Alps?
Conditions. Where is the flat land within 500 m of the highway?
Implications. If we build a theme park here, what will be the effect on traffic flows?
Types of GIS architecture
- Desktop (stand alone desktop with GIS files)
- Centralised desktop (Desktop sharing files to other PC’s over LAN)
- Client-server (data base to be accessed by PC’s only via WAN)
- Centralised server
- GIS app server accessable on PC’s Browsers, Devices, Web
- For multinational companies
continuous and discrete GIS data e.g
continuous: distance to classes
Discrete: bus timetable
Data model simply is
-set of constructs for representing objects and processes (geographical features) in the digital environment of a computer
Data model components
Reality–>Conceptual model (Partially structured model e.g buildings in a campus)–>Logical model (Diagrams and lists e.g buildings connected to roads)–>Physical model (GIS representation: tables with compiled data, legend)
Increasing level of abstraction from human orientated to computer orientated.
Digital ELevation model is ___ data
contin
watersheds, streams and waterbodies are ____ data
discrete
Raster data is most useful for representing:
continuous fields:
e.g elevation, temperature, soil type, land use
Vector data is most useful for representing
discrete objects:
e.g property lines, political boundaries, transportation.
Vector data models consist of ___, ___ and ___
Points, lines and polygons (shape files)
raster data model is based on ___
a grid of cells
cells values are represented as numbers in a database, each number defining a land use (for e.g).
Attribute data
-link spatial attributes with thematic attributes (non-spatial)
Vector is more accurate than raster T/F?
True
- raster cell size is bigger than exact vector location
e.g raster data sources
-remote sensing (LANDSAT, SPOT), scanned maps, DEM
e.g vector data sources
- census data (tabular)
does changing raster to vector data increase accuracy?
no because it the vector is simply joining the center of each cell.
Modifiable Areal Unit Problem (MAUP)
- Effect of geographic unit size and shape on geographic patterns:
1. Scale effect
2. Zoning effect
Three elements of topology
Adjacency, connectivity and containment (enclosure)
Adjacency
when two polygons share the same boundary
Connectivity
multiple lines are connected at one point (node)
Containment
one polygon contained within another poligon
Geographic coordinate systems
- defines unique points on the earth’s surface
- Longitude and latitude
- referenced to a datum
which type of latitude requires knowledge of the earth’s shape (ellipsoid)
Geodetic
standard ellipsoid datum: WGS84
Projected coordinate systems
-transforms a 3D Geographic Coordinate System to a flat coordinate system
Secondary data:
- OpenStreetMap
- Digital globes (nearMap)
- online datasets
- Remote sensing (LiDAR)
GIS question example: Nuclear Waste Disposal
a) what data?
b) where data (primary+secondary)
c) Data model used and why
a) -geology of the region so that nuclear waste is not stored near potentially reactive materials or unstable rock types or near minerals that could potentially be mined in the future.
- transportation routes: to identify where there is sufficient transport routes to waste site
-population: ideal site should be away from pop. centres
- conservation areas: top avoid
-watershed: no radioactive waste to enter water course.
b) roads–>openstreep map/AURIN
population–>census
conservation–> Qspatial
geology–> qld gov
primary data-insitu vector data capture–> chosen site measuring angles and dists. from known points
c) Vector data analysis. Find intersection of suitability criteria i.e geology type, adequate trnasport infrastructure, outside conservation areas, away from pop.
Primary Data
In-situ data capture
- GPS
- Ground Surveying (
- Location based service
- Digitizing (on screen)
Remote sensing- resolution
Spectral resolution
Secondary vs primary data
- primary more expensive
- secondary is vast and readily available
resolution in remote sensing
spectral resolution: colour spectrum
spatial: size of each pixel corresponding to the real ground
temporal resolution: intervals of scanning
Radiometric resolution:
types of transformation in georeferencing
-Affine: 3 points needed
-second order polynomial: 6 points needed
third order polynomial
Root mean square error
assess “goodness-of-fit” to control points but NOT non-control point distrotion
types of measurement errors
- Positional accuracy
- attribute accuracy
- logical consistency
- completeness
positional accuracy
expected difference in the measured geographic location of an entity from its true ground position
Absolute accuracy (within positional accuracy)
accuracy with respect to a coordinate system
Relative accuracy (within position accuracy)
accuracy with respoect to position of geographic entities relative to each other
attribute accuracy
of non-spatial attributes of geographic features (e.g land classification: grass where buildings are)
logical consistency
faithfulness of the data structure. Spatial data inconsistencies: incorrect line intersection, duplicate lines or boundaries or gaps in lines.
completeness
e.g holes in data, unclassified areas.
metadata
data about data: -how, when, where and who collected data
- scale of data
- coordinate system
- data quality and accuracy
data quality: scale–> extent and resolution
extent is size of study area
resolution is size of geographical units (cell size)
data sharing requirements
- strict metadata standards
- standard data formats for transferability among platforms
- data sharing agreements
- portals for access and storage of data
2 classes of GIS Questions
-Normative (practical or decision-making/design applications). e.g where to site a nuclear plant
- Positive (Discovery or the
Advancement of Science). e.g where is global warming impacting most
