Module Review Flashcards
What are the 6 core components of a GIS?
- Network
- Software
- Data
- Procedures
- Hardware
- People
How can you define GIS?
“a system for capturing, storing, checking, integrating, manipulating , analysing and displaying spatial data from the real world for a particular set of purposes.”
“a set of tools for collecting, storing, retrieving at will, transforming, and displaying spatial data from the real world for a particular set of purposes.”
3 types of GIS systems
GIS
GIScience
GIStudies
What is spatial data?
Data that defines something about a location.
Location = where?
Attribute - what?
What is vector data?
A representation of the world using points, lines, and polygons.
Vector models are useful for storing data that has discrete boundaries, such as country borders, land parcels, and streets.
What are attributes?
A database or table linked to each vector feature
Can contain only an identifier or a large amount of additional data
What are spatial queries?
What is at A? A can be - A single feature - Features defined by distance - Features within areas
What are attribute (aspatial) queries?
Where is B true?
Query attribute data
- Structured query language
- Raster attribute table can be called reclassification
- Create new raster data set from results
What is topology?
Looks at geometric characteristics and relationships.
- connectivity
- adjacency
- containment
- distance
What is raster data?
Useful for continuous data
A grid of pixels or cells where each cell has a single numeric value.
What is the resolution of raster data?
refers to the area/ size of the cell/pixel
Examples of raster data?
Scanned maps
Aerial photography
Surfaces (elevation, house prices)
Raster precision/ resolution
Higher precision =
…smaller cell size
More cells required for same coverage
More detail
More processing power
What are data layers?
Each layer references a dataset and specifies how that dataset is portrayed using symbols and text labels.
Location and attribute
Layers can be combined visually
Information can be extracted from attributes based on location
What are map projections?
Why?
Method to represent the surface of the earth.
Creates maps and enables easier measurement
Different types of map projections?
Cylindrical
Azimuthal
Conic
What is a tangent projection?
A projection whose surface touches the globe’s without piercing it.
At the point or line of tangency, the projection is free from distortion.
What is a secant projection?
Two lines of minimal distortion creating parallel secant lines.
Why is there no distortion in tangent/secant projections?
Scale at tangent and secant lines.
What is a transverse mercator?
Transverse cylindrical projection.
Distances are only true along the central meridian
Accuracy reasonable within 15 degrees of the meridian
Used for national to large scale mapping.
Spatial referencing
Geographic co-ordinate systems
Latitude and longitude
Spatial referencing
Cartesian co-ordinate systems
OS National grid
Spatial referencing
Geocodes
Postcodes (descriptive/ text location)
Raster symbology
Interval and ratio data
Colours/ shading = progression
Reinforced with legend
Two main types of map
Topographic- reference maps with lots of different types of information
Thematic- relates to a topic e.g crime
Representations of spatial data
3D visualisation
Cartograms
Schematics
Key elements of a map output
Reference grid Map body Title North arrow Legend Scale Inset map Map metadata Copyright acknowledgment
Large scale features
Covers small areas
Large amount of detail
1:1000
1:25000
Small scale features
Covers large areas
Small amount of detail
1:250,000
1:1,000,000
Types of scale
Ratio: Units do not matter as long as they are the same
Verbal (nominal): 1 cm = 1 km
Graphical
Types of generalsiation
Simplification Enlargement Displacement Combination Selection (elimination) Classification
Measurement of length
Pythagorean
Great circle
Manhatten
What is the pythagorean measurement of length?
Straight line (euclidean) distance between two points on a flat plane
What is the great circle measurement of length?
Gives the shortest distance between two points on a spherical globe given their latitudes and longitudes
What is the manhattan measurement of length?
Linked to raster data
The sum of horizontal and vertical components when measuring a diagonal.
What is an issue with vector length measurement?
Length of a true curve us almost always longer than length of poly line.
What is the raster measurement of area?
Area = no of cells x cells area
What is an example of a vector measurement?
Buffers
What is an example of a raster measurement?
Euclidean distance
Each cell gives a distance to the closest source cell.
What is reclassification?
Creation of new output later based on values in input layer.
Input: may be categorical or continuous
Output: Generally categorised
How to to reclassify something.
Spatial analyst > reclass > reclassify
Vector overlay
Comparison of layers which occupy same space
Select by locations (select features)
Used to create new data (geoprocessing tools)
Types of vector overlay
Clip
Intersect
Union
Basic cartographic modelling
Simple case
Input layer -> Single operation -> output
Basic cartographic modelling
Complex case
Multiple input layers -> multiple operations -> output
Data conversion
Raster to vector:
Vectorisation
Data conversion
Vector to raster:
Rasterisation
Data conversion
Change in feature type:
Points to area: Aggregation
Why are data storage: data base important?
For storing, organising, analysing and retrieving data
Types of data errors
Positional accuracy (precision- probable location e.g +/- 5m)
Attribute accuracy
Representations of reality
Errors in data collection
Sampling mistakes (technical difficulties, incorrect operation recording) Sampling bias
Remote sensing
Shadow =
Cloud distortion
Accuracy
The extent to which an estimated data value represents its true value
Consists of two components:
Precision
Unbiasedness
Precision
Specificity (e.g number of decimal places or significant features)
The dispersion of a measured or predicted value
Bias
Any systematic difference between the true value and the measured or predicted value.
Three key types of accuracy in GIS
Positional
Attribute
Topological
What is positional accuracy?
Are features in the right place?
What is attribute accuracy?
Do features have the correct value (continuous/ categorical)
Benefits of GIS
Direct
Savings
Increased effectiveness
Brand new products
Benefits of GIS
Indirect
Improved information sharing
Greater understanding
Better justification
More competitive
Costs
Direct
Hardware/software
Data
Human and administrative costs
Costs
Indirect
Increased reliance on computers
Higher skilled workforce required
What is ecological fallacy?
Falsely attributing characteristics of a zone to individuals on the basis of their membership to that zone
Very common problem in the social sciences
Can lead to wrong conclusions about causality
Geovisualisation
What3words
Traditional maps- limitations
Cartograms
Other visualisations
