8: Spatial Data Models

Question 1

UNDERSTAND THE FUNCTIONS OF A MODEL

Answer 1

Mapping - mappings, from representations of natural or artificial originals that can be models themselves

Reduction - of attributes from the original that seem relevant to model creators and/or model users

Pragmatism - not only a model of something but relating to fitness for users, purpose and time

Question 2

LIST LEVELS OF GIS DATA MODELLING ABSTRACTIONS

Answer 2

1. Reality
2. Conceptual model
   - human oriented
   - views of the world: entities, fields
3. Logical model
   - computer oriented
   - data structure: raster, vector, objects
4. Physical model

Question 3

BASIC GIS DATA MODELS AND DATA STRUCTURES

Answer 3

CAD - engineering design
Graphical - simple mapping
Image - image processing and analysis
Fields: raster/grid - spatial analysis/modelling
Network - network analysis
Geo-relational - geo-processing geometric features
Entities: TIN - surface / terrain analysis / modelling
Entities: Objects - features with behaviour

Structure: raster or vector

Question 4

UNDERSTAND TOPOLOGY

Answer 4

How are entities related…

Knowing where features are in relation to other features (connectedness of points, lines and aerial features)

Science and mathematics of geometric relationships

Question 5

DATA MODELLING PROCEDURE BASIC ELEMENTS

Answer 5

1. What needs to be modelled?
2. What kind of basic real world features and relationships?
3. Which kind of model type?
4. What kind of relationships?
   (1: 1 or many to 1 or 1 to many)
5. What kinds of properties do features have?

Question 6

3 kinds of topology

Answer 6

Adjacency - shared node/edge
Connectivity - network connections at nodes
Containment - one object within another

Question 7

What is topology important for?

Answer 7

Data validation - checking consistency

Spatial analysis - network tracing, spatial queries, etc

Question 8

How is topology described in GIS?

Answer 8

Table for points with ID and x,y
Table for chain/segment with ID for each line with start and end node, poly to left and right, and length
Poly structure table with ID and chain segments that create it
Poly attribute file with ID and variable + name

Question 9

How are areal features (points, lines and polygons) and topology modelled and stored in vector models?

Answer 9

Table for nodes with ID and x,y
Table for chain/segment with ID for each line with start and end node, poly to left and right, and length
Poly structure table with ID and chain segments that create it
Poly attribute file with ID and variable + name

Question 10

How are TINs modelled and stored in vector models?

Answer 10

Each triangle has an ID and has a list of the three nodes (by their ID) which create it and the adjacent neighbours.

Triangles always have three nodes and usually have three neighbours unless they are at the edge of the data.

Question 11

Object oriented data model

Answer 11

A collection of geographic objects and relationships between objects

Object classes:
-include both state (attribute and properties) and behaviour (methods defining what the object does)

Encapsulation
-objects are packaged with states and behaviours

Inheritance
-reuse of states and behaviours in other objects

Polymorphism
-individualise states and behaviours for each object

Question 12

Modelling issues to consider

Answer 12

Data modelling is an art, and a science, and uses technology

Data modelling expertise evolves over time

Each model is unique and depends on the use case, users and purpose

Each model needs to be designed with a particular tool kit in mind

Modelling takes time and needs input from users and stakeholders