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.
Types of Attribute Tables
- Feature Attribute Table (FAT)
Has access to spatial data, stores features geometry.- Non-spatial Attribute Table
Not directly connected to the spatial features,
- Non-spatial Attribute Table
Two ways you can get data into GIS
For raster: scanning an image or using an ariel image
For Attributes: created manually in the GIS environment or import a dataset from somewhere else
What is digitizing?
Process of converting data from analogue to digital format (paper to computer)
Name 5 data input errors
Eyesight, perception and intelligence, mistakes, copying and translation, operational training skills, hand movement
GPS
Global positioning system
What does DBMS stand for?
Database Management System: a collection of software that manages the database structure and control access to data stored in a database.
What does data independence mean for DBMS?
Users interact with a representation of data independently of the actual physical storage.
The DBMS is in charge of translating the user’s manipulations into efficient operations on physical data structures (isn’t saved until the user does so).
What is an Entity?
The object of interest (often called entities)
What are the advantages of using a relational database?
Each table can be prepared, edited, and maintained independent of each other.
Tables can remain separated until a query (eg, how many students live at this post code).
Links are also temporary and easily modified. Changes as the data are modified and changed.
What does an ER (Entity Relationship) diagram show?
See potential issues.
- Entities and their relationships
- Degree of a relationship
- What data needed to be stored and captured
- Ambiguities
What are the four table relationships (database design)?
1) Flat file
2) Hierarchical
3) Object Oriented
4) Relational
What is topology?
How layers convey spatial relationships.
List four types of spatial relationships?
- Connect
- Adjacent
- Contained
- Interest
- Near
- Difference
Relative position
What is a geodatabase?
Centralised storage of data. Native to ArcGIS. Container for spatial and attribute data. Contains feature classes.
Shapefile vs Feature Class
Shapefile: single feature class which exists outside geodatabase.
Feature Class: the most basic level of spatial data. Has one geometry type, including point, line, and area.
What is a feature dataset?
A way of storing feature classes together. Allows us to include topology rules (eg, manholes must align with sewerlines).
List four field types
- Text
- Date
- Short (eg, 16)
- Long (eg, 142568)
- Blob (can be an image - chunks of binary data, storing images, multimedia, and geometry of spatial features)
- Float (eg, 9.8)
Double (longer float)
What are the four data types?
Ratio: absolute zero
Interval: no absolute zero
Ordinal: ordered categorises
Nominal: categories
Why do we use SQL?
Uniformly used in all relational systems, Declarative, and Simple and accessible to non-experts. Good for data manipulation.
What does AND do?
Selects the data point with both variables
What does OR do?
Selects the data point with one or the other
List 3 benefits of cloud computing
Lower total cost of ownership, increased availability, scales by demand
What is cartography?
The art, science, and techniques of making maps or chart.
What are the map design essentials?
purpose and medium, linking layout to map purpose, planning a layout, choosing appropriate export options, scale, map projection, map symbols, output methods
What is a visual hierarchy?
The map’s purpose determines which of its elements are most important. They should be displayed more prominently. Size and position important.
What are the map types based on function?
General reference maps ( used for general purposes and will display a variety of spatial features, including boundaries, settlements, landcover), thematic maps (Aimed to show the spatial distribution or pattern of a particular theme).
How many visual variables are there?
6
Hue, texture, shape, size, intensity, and value.
What are the basic qualities of colour?
Hue: The quality which distriguishes one colour from the next (blue, red green)
Value/shading: How light or dark you make the colour
Chroma/saturation: How rich you set your colour (grey = low chroma, full saturation = high chroma)
Hue (Quality of Colour)
The quality which distriguishes one colour from the next (blue, red green)
Chroma/Saturation (Quality of Colour)
How rich you set your colour (grey = low chroma, full saturation = high chroma)
Value/Shading (Quality of Colour)
How light or dark you make the colour
What does CYM and RGB stand for?
Different export types.
Cyan Yellow Magenta
Red Green Blue
Name the different mapping methods?
Chart, Daysmetric, Choropheth, Isarithmic, Flow.
Can’t discuss, cat in fence
Daysmetric Map Method
Similar to choropleth, except that the shading or colour coding follows areas with homogeneous values rather than administrative units.
Choropleth Map Method
Useful for displaying quantitative data. The process involves the use of symbology such as shading and colour within administrative units. Each unit is coloured/shaded according to data held with an associated attribute table.
Chart Map Method
Applies the use of pie symbols or bars or some kind of chart protocol to display two sets of (related) quantitative data.
Flow Map Method
Shows or displays different quantities of flow (usually linear). Differing line widths indicates flow volumes.
Can include choropleth map underneath.
Isarithmic Map Method
Uses a series or a system of isolines to represent a surface
Contour line maps are created using a series of x,y points and associated values. Lines of equal value are drawn or estimated using a system called Spatial Interpolation.
What is Spatial Analysis?
Set of methods whose results do not vary under changes in the locations of the objects being analysed.
What does Overlay do?
Operations which involves two separate polygon layers formed as one. Attributes from both feature layers are carried from each layer and combined into a single attribute table.
What are the types of Overlay?
Union, intersect, symmetric difference, identity.
What does Dissolve do?
Aggregates features, or removes boundaries, based on specific attributes
What is Buffering?
Creates new polygons by expanding or shrinking existing polygons or by creating polygons from points.
Why are process diagrams important?
Record the processes undertaken, or allow for someone else to do it.
What does reclassify do?
A function that takes input cell values and replaces them with new output cell values.
What is an overlay?
Boolean operators or arithmetic operators
Boolean operators (And, Or, Not)
Arithmetic operators (+, -, /, *)
What is remote sensing?
Interpretation of measurements of electromagnetic energy reflected from or emitted by a target from a vantage-point that is distant from the target.
What can you use low pass and high pass filters for? (Image Enhancement)
High pass filter: small-scale changes
Low pass filter: large-scale changes
What does raster calculator do?
Combination of data layers to produce new feature geometry, where overlap occurs. Works on single layers.
What does image classification do?
Pulls the spectral signatures of focus data, gives indication of density.
What is spatial interpolation?
procedure of estimating the values at unsampled sites within an area covered by existing observations”
What are the two types of processes that cause clustering?
First order processes: points located independently resulting in varying density
Second order processes: interaction between points, either attraction or repulsion
What methods can you use for spatial interpolation?
Thiessen polygons, B-Spline, Inverse Distance Weighted, Krignig
What is Tobler’s First Law of Geography?
everything is related to everything else, but near things are more related than distant things.
What is spatial autocorrelation?
Measures the relationship between two random variables.
‘Auto’ indicates that the measurement of the correlation is done with the same random variable, measured in different places in space. Do they cluster, or disperse, or are they random?
What does Moran’s I test for?
Measures spatial autocorrelation based on feature locations and feature values simultaneously.
- Random
- Clustered
- Dispersed
What is GWR?
Geographically Weighted Regression. Allows user to not hold the relationship constant over the study area, in exchange for localised regressions. Can identify residuals for interpretation on where differences lie. Gives hint to which variables are missing from your analysis.
Spatial Interpolation: B-Splines
Output data structure is points on a raster. Best for smooth surfaces (eg, income)
Not common in GIS software, because it smooths so much.
Spatial Interpolation: IDW - Inverse Distance Weighted
Method most often used by GIS analysts. Uses Tobler’s first law. Gives greatest weight to closest points to the unsampled sites.
Limits range of values by regression to mean, pulling data to the central value.
Bad for elevation, where high places are less likely to be sampled. Good for rainfall.
Spatial Interpolation: Krignig
Optimal method of interpolation for use in mining industry, which requires the greatest understanding of the dataset.
Based on the rate at which the variance between points changes over time.
- Rate is shown in the variogram which displays how the average difference between values at points changes with distance between points.
What is geocoding?
process of assigning spatial locations to data stored in tabular format with some fields (eg, postal address) describing their location.
Address Geocoding
a type of geocoding which involves a way to plot street address information as point on a map
Requires TWO sets of data:
- Individual street address in a table
- Reference database with street information on a map and information about postcodes, street names, addresses, etc assigned to line segments.
Reclassify Outputs?
Altitude, slope, aspect, solar radiation, hillshade
What are the methods of network analysis?
- Shortest path problem
Shortest distance. Looks at impediments to travel (raster). Networks in vector can offer greater flexibility. Several paths considered.- Travelling Salesperson Problem
A salesperson needs to visit a specific set of clients in a day and to do so by the best route (usually not the quickest, but cheapest) - Location Allocation Modelling
Model supply and demand through a network - Route Tracing
Trace flows of goods, people, services, and information through a network. Particularly useful if unidirectional.
- Travelling Salesperson Problem
Legal vs Ethical Conduct
Legal Conduct: defined by the documented and recorded findings of our legislatures and courts.
Ethical Conduct: involved in the choices users make in applying geographic information system technologies. Is also involved in the choices scientists and researchers put their time and the knowledge base they help advance.
What’s Ethically Wrong?
- Misrepresenting data (deliberately/data not available, for the greater good/private interest).
GI Military Applicants: does it depend on the country? American/dictatorship/NZ
Landmine location database: Red Cross for removal, insurgents.
GIS As a Problem Solver
- Whose problems are being solved?
- Who defines these problems?
- Who is involved in the generation of solutions?
- For whom are these solutions valid and good?
How do alternative approaches to problem solving or resolution fit in?
What is usability?
Quality attribute that assesses how easy user interfaces are to use
What does FOSS stand for?
Free Open Source Software
freedom to reuse and copy, NOT price of software.
SQL
Structured Query Learning
