Lecture 5 Flashcards
What does spatial mean?
Where
What does thematic mean?
What
What does temporal mean?
When
What are the transformation stages within GIS?
Real World -> Raw Data (data collection)
- > Data model (data manipulation)
- > Output data
Primary data capture
Raster
Remotely sensed data
Satellite imagery
Aerial photography
Wireless sensors
Primary data capture
Vector
Land Surveys
Global positioning systems (GPS)
Secondary data capture
Raster
Scanning
Secondary data capture
Vector
Digitising
What is Aerial photography?
Snapshot of earth at a particular time
Cameras mounted in airplanes flying at low altitude
Useful for background/context or can be transformed into actual objects
Advantages of aerial photography
Widely available
Cheaper than satellite images
Good for monitoring change/ sequence of events
Goof for large scale, small area projects
High spectral, spatial and temporal resolution
Can create 3D images by overlapping images
Disadvantages of aerial photography
Not spatially referenced – have to be geo-referenced
Scale distortion – have to be geo-rectified
Susceptible to daily/seasonal/annual changes in features
Primary data capture
Land Surveys
Primary vector data capture
Measures angle and distance from known points to establish 3-D location
Increasingly automated
Time-consuming & expensive but accurate
Secondary data capture
Digitising
- Manual digitising
- Table digitiser & PC or on-screen
- Registration/TIC points
- Point & stream modes
- Time-consuming
- Requires extensive editing, cleaning & error-checking
Digitising errors depend on
- Scale & resolution of source map
- Quality of equipment/software
- Skill/experience of operator
- Quality of editing process
Data conversion
•Change in data model:
–Raster to vector: vectorisation
–Vector to raster: rasterisation
Data conversion
•Change in feature type:
–Points to areas: aggregation
Data storage: databases
Databases important in GIS to store, organise, analyse and retrieve data
Tables
Columns – attributes to be stored (fields)
Rows – values of attributes for each spatial feature
Keys – the field/attribute used to uniquely identify each feature, often used to join tables
Relations – relationships/links between tables/records
What is Structured Query Language (SQL)?
- Standard language for querying databases
* Sets of logical expressions
Structured Query Language (SQL)
Pseudo-English-language style
–Select land plots where owner = ‘Smith’
–Select hotels where street name like ‘High St.’ and rooms > 40
–Order by population
–Update table set population density = population / area
–Mathematical expressions: exp(), log(), sqr()
–Relational joins
•Many are now menu/wizard based e.g. MS Access
What are spatial queries?
…where?
Which towns are within 5 miles of Happy Valley?
Aspatial queries … what?
How many days in the year had a temperature below 0 ºC?
GIS queries usually combine elements
of both spatial and aspatial queries
Identify the spatial and aspatial parts of this query…
Which five-star hotels are within 5 miles of the University?
Which five-star hotels (aspatial)
are
within 5 miles of the University? (spatial)
Identify the spatial and aspatial parts of this query…
What is the shortest route from Southampton to London, without using any motorways?
What is the
shortest route from Southampton to London, (spatial)
without using any motorways? (aspatial)
Identify the spatial and aspatial parts of this query…
Which towns fall within land which is designated as National Park?
Which towns fall within land (spatial)
which is
designated as National Park? (aspatial)
