GIS L1 afternoon (Monday)
Describing reality
Thematic description (what) geometrical description (where) temporal description (when)
Data model = captures choices made by scientists and others creating digital representation of phenomena.
1. Spatial perception = understanding what to store in the dataset.
- What are the objects considered
- What do you need to consider an object
- To what detail to consider these objects
2. Information model = what aspects of where, when etc.
3. Data structure = assign tables
4. Database & application
Spatial perception
Thematic, categorical and discontinuous
Discrete = boundaries, within the boundary same
characteristic
Continuous phenomena = characteristics function of
location. At each location the characteristic is different.
elevation map.
Tangible phenomena = things that are very present .
everything you see on a topographical map. (google maps)
Virtually phenomena = statistical neighborhoods, do not
exist in real world. But can be represented in a map.
Spatial representation = formal description of perceived phenomena that are subject to scientific research
Continuous field location determines values
Discrete objects boundary determines values
Two approaches: raster and vector (can be used to store objects and fields).
Objects in the vector data model
Point
- only location important
- No dimensions
- 0 dimension
Line
- 1 dimension
- Location, length, shape
- Roads and streams
Area
- 2 dimension,
- Location, length, area and shape
- Beginning and end
- E.g. waterbodies
1
,Vector = represented as a point.
Raster = consist has matrix or square cells. Aerial photographs, or satellite.
Point = single cell
Line = sequence of neighboring cells
Area collection of contiguous cells
L2 morning (Tuesday)
Attribute = name, species, age of tree
Features = area of land (land use)
Features can be explained in vector or raster (cells have same function)
Geometry
Location and orientation (coordinate system)
- X and Y
Shape and size
- Rectangular, triangular etc. It can have a size and length
Topology = how entities are related to each other in the real
world. Or spatial relationship between objects and between
primitives of the geometry representation ( points, line etc.)
- The wardrobe words, from-to, inside-outside
- Relative location of spatial objects
- Invariant for coordinate transformation
- Relations: point-point, point-line, point-area
How stored in GIS
Relative relations between objects, don’t change when coordinate change
Shape file
Shape file has no topology
Qualitive = what is it and what is the order
nominal difference text field
Ordinal order higher, lower
2
, Quantitive
Interval doesn’t have an absolute point of zero, can go below 0 (degrees Celsius)
Ratio = cannot below 0. (speed in m/s)
Relational data model = collection of tables that can be related to
each other by key attributes who values uniquely identify a record
in a table.
Two tables can be joined when 1:1 or many : 1. A primary key has
to be defined. This is when they have a share attribute. Related
tables the unique identifier connect to other identifier 1: many.
Merge = database system creates its own primary key.
Raster
Integer raster (location based) whole numbers
- Nominal, ordinal
- Discrete data/ discontinuous building, lake
- Value attribute table
Floating point rater = number with decimals
- interval ratio
- Continuous data
- No value attribute table = value itself has the meaning of the phenomena itself. The values can be
infinite lake depth
Region = cluster of cells with the same value
Zone = all regions with the same value
L2 afternoon
How to get data
Harvesting data by the web
- Portals: data framework
- Spatial data infrastructure = technology, policy, standards
- Meta data
Handling
In situ (field measurements)
SDI = coordinated series of agreements on: standards, policies and technologies to support efficient use of geo-data.
Facilitation and coordination of finding, exchange and sharing (accessible) of geodata.
The people are the users of the data. Inspire is the European Union spatial data infrastructure, to make sharing spatial
information with public sector better and facilitate public accesses.
Web service has 3 levels: accesses of web services, interoperability by web services, servers with data and metadata.
- Web map service = visualize the data, but no download feature (kinda pdf)
- Web feature service = download, visualize and edit data
Meta data = description of the data
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