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Prof. Qiming Zhou GIS Data Modelling GIS Data Modelling.

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Presentation on theme: "Prof. Qiming Zhou GIS Data Modelling GIS Data Modelling."— Presentation transcript:

1 Prof. Qiming Zhou GIS Data Modelling GIS Data Modelling

2 GIS data modelling What is a data model? GIS data models
Prof. Qiming Zhou GIS data modelling What is a data model? GIS data models CAD, graphical and image GIS data models Raster data model Vector data model Object data model GIS Data Modelling GIS Data Modelling

3 What is a data model? The heart of any GIS is the data model.
Prof. Qiming Zhou What is a data model? The heart of any GIS is the data model. A data model is a set of constructions for describing and representing selected aspects of the real world in a computer. There is no single type of GIS data model that is best for all circumstances. GIS Data Modelling GIS Data Modelling

4 The role of a data model in GIS
Prof. Qiming Zhou The role of a data model in GIS Operational GIS Analysis and Presentation GIS Data Model Description and Representation Real World People Interpretation and Explanation GIS Data Modelling GIS Data Modelling

5 Levels of data model abstraction
Prof. Qiming Zhou Levels of data model abstraction Reality: real world phenomena Conceptual model: human-oriented model of selected objects and processes in relevance, often partially structured Logical model: implementation-oriented representation of reality, often expressed in the form of diagrams and lists Physical model: portrays the actual application in a GIS, often comprises tables stored as files or databases. GIS Data Modelling GIS Data Modelling

6 Levels of abstraction Reality Conceptual model Logical model
Prof. Qiming Zhou Levels of abstraction Reality Human-oriented Conceptual model Increasing abstraction Logical model Computer-oriented Physical model GIS Data Modelling GIS Data Modelling

7 Conceptual model GIS Data Modelling Road Line Area Attributes
Centre line Network Intersection Main section Shoulder Speed limit No. of Lines A road: Centre line (position) Edge line (width) Shoulder Number of lanes One way/two way Speed limit Traffic conditions Pavement Underground structure Intersections Date of completion Maintenance date … … GIS Data Modelling

8 Logical model GIS Data Modelling Road Line-id Area-id Road No. Name
… … S-Node E-Node Vertices Length Left edge Right edge Pavement Area x,y, …, … … GIS Data Modelling

9 Physical model Road GIS Data Modelling Road R-… R-line R-area … …
Record 1 Line-id Area-id Road No. Name Record 2 Record n File: Road Record 1 S-Node E-Node Vertices Length … … Record 2 Record n File: R-line GIS Data Modelling

10 GIS data models CAD, graphical and image GIS data models
Prof. Qiming Zhou GIS data models CAD, graphical and image GIS data models Raster data model Vector data model Object data model GIS Data Modelling GIS Data Modelling

11 Geographical data models used in GIS
Prof. Qiming Zhou Geographical data models used in GIS Data model Application Computer-aided design Simple mapping Image Image processing and simple grid analysis Raster/grid Spatial analysis and modelling Vector/geo-relational topological Operations on vector geometric features Network Network analysis Triangulated irregular network (TIN) Terrain analysis Object Operations on all types entities GIS Data Modelling GIS Data Modelling

12 CAD, graphical and image GIS data models
Prof. Qiming Zhou CAD, graphical and image GIS data models The earliest GIS were based on very simple models. CAD data model: Local drawing coordinates Objects do not have unique identifiers. No relationship details between objects are stored. Simple graphical data model: cartography Image model: field data rather than objects. GIS Data Modelling GIS Data Modelling

13 Prof. Qiming Zhou The CAD data model A CAD model focuses on feature drawing only so that it does not represent any kind of relationships between objects. GIS Data Modelling GIS Data Modelling

14 Simple graphical data model
Prof. Qiming Zhou Simple graphical data model A simple graphical data model is adequate to make a cartographic representation of Hong Kong SAR. GIS Data Modelling GIS Data Modelling

15 Prof. Qiming Zhou Image data model Image data: On the left is the false colour composite of Landsat ETM image using Band 4, 3 and 2. On the right is the classification of the image using 6 bands of the Landsat ETM images (excluding Band 6). GIS Data Modelling GIS Data Modelling

16 Prof. Qiming Zhou Raster data model Raster data model uses an array of cells, or pixels, to represent real-world objects. Difference between raster and image data models: Image data do not have attribute table attached so that they have only one attribute field. Raster data have attribute table that can be joint to other tables so that they can have multiple attribute fields. Applications: image data: image processing; raster data: spatial analysis and modelling GIS Data Modelling GIS Data Modelling

17 Grid with attributes GIS Data Modelling Prof. Qiming Zhou

18 Data structure of raster data model
Prof. Qiming Zhou Data structure of raster data model Cartographic model (database) Map layer (overlay, coverage, grid) Zone (region) Location GIS Data Modelling GIS Data Modelling

19 Hierarchy of the raster data structure
Prof. Qiming Zhou Hierarchy of the raster data structure Cartographic Model Map layer Zone Orientation Resolution Title Value Label Location Row coordinate Column coordinate GIS Data Modelling GIS Data Modelling

20 Prof. Qiming Zhou Cartographic model The data for an area can be visualised as maps or layers. A cartographic model is a set of data describing selected characteristics of each location within a bounded geographic area in the form of map-like layers. GIS Data Modelling GIS Data Modelling

21 Cartographic model (cont.)
Prof. Qiming Zhou Cartographic model (cont.) Buildings 3 1 2 1 2 3 Forest types 1 2 3 Soil types Topography Soils Real world GIS Data Modelling GIS Data Modelling

22 Prof. Qiming Zhou Map layer A map layer is a set of data describing a single characteristic of each location within a bounded geographical area. Only one item of information is available for each location within a single layer. Major components of a layer are its resolution, orientation and zones. GIS Data Modelling GIS Data Modelling

23 Map layer (cont.) Australia GIS Data Modelling Prof. Qiming Zhou
New South Wales Victoria Queensland South Australia West Australia Tasmania Y X Northern Territory N GIS Data Modelling GIS Data Modelling

24 Prof. Qiming Zhou Zone A zone is a set of contiguous location that exhibit the same characteristic. Term class is often used to refer to all individual zones that have the same characteristics. Major components of a zone are its value, label and locations. GIS Data Modelling GIS Data Modelling

25 Zone and class 2 1 3 4 5 8 9 6 7 10 11 12 Zone number Class A Class B
Prof. Qiming Zhou Zone and class Class A Class B Class C Class D Class E 1 2 3 4 5 6 7 8 9 10 11 12 Zone number GIS Data Modelling GIS Data Modelling

26 Value and label of a zone
Prof. Qiming Zhou Value and label of a zone Value The item of information stored in a layer for each cell or pixel Cells in the same zone have the same value Label “Additional” information associated with each zone Can be numeric or alphabetic (i.e. numbers or text) GIS Data Modelling GIS Data Modelling

27 Zone (cont.) Australia GIS Data Modelling Prof. Qiming Zhou
State ID State Name Capital Population 02 New South Wales Sydney 07 Queensland Brisbane Zone (cont.) Australia New South Wales Victoria Queensland South Australia West Australia Tasmania Y X Northern Territory N GIS Data Modelling GIS Data Modelling

28 Prof. Qiming Zhou Location A location is the smallest unit of geographical space for which data a recorded (also called cell or pixel). A location is defined as that a portion of the cartographic plane is uniquely identified by an ordered pair of coordinates (row and column numbers). GIS Data Modelling GIS Data Modelling

29 Vector data model Simple features Topological features
Prof. Qiming Zhou Vector data model Simple features Topological features Network data model TIN data model GIS Data Modelling GIS Data Modelling

30 Vector representations
Prof. Qiming Zhou Vector representations point line area Scale city wells highway political boundary streams agriculture land urban land airport GIS Data Modelling GIS Data Modelling

31 Multiple representation
Small-scale representation of cities as points Large-scale representation of cities as areas GIS Data Modelling

32 Simple features Point number x, y coordinates
Prof. Qiming Zhou Simple features 1 2 4 3 Point number x, y coordinates 1 (2, 8) 2 (3, 3) 3 (12, 7) 4 (9, 4) 2 1 Line number x, y coordinates 1 (1, 6), (4, 8), (8, 6), (13, 8) 2 (1, 3), (4, 4), (9, 2), (13, 5) 2 1 Polygon number x, y coordinates 1 (2, 5), (3, 8), … (2, 5) 2 (6, 4), (8, 4), … (6, 4) GIS Data Modelling GIS Data Modelling

33 The “spaghetti” structure
Prof. Qiming Zhou The “spaghetti” structure 10 63 64 23 Original map Map expressed in Cartesian coordinates 63 64 23 10 Feature Number Location Point Line Polygon X Y (single point) X1 Y1, X2 Y2, …, Xn Yn (string) X1 Y1, X2 Y2, …, X1 Y1 (closed loop) 10 23 63 64 GIS Data Modelling GIS Data Modelling

34 Prof. Qiming Zhou Topological features Topological features are simple features structured using topological rules. Topology is the science and mathematics of relationships. In GIS, topology is used to validate the geometry of vector datasets. GIS Data Modelling GIS Data Modelling

35 Prof. Qiming Zhou Arcs When planar enforcement is used, area objects in one layer cannot overlap and must exhaust the space of a layer. Every piece of boundary line is a common boundary between two areas. The stretch of common boundary between two junctions (nodes) may be called edge, chain, or arc. Arcs have attributes which identify the polygons on either side (“left” or “right”). In what direction by which we can define “left” or “right”? Arcs are fundamental for topological features. GIS Data Modelling GIS Data Modelling

36 Arcs (cont.) An Arc vertex End note Start node GIS Data Modelling
Prof. Qiming Zhou Arcs (cont.) Start node End note vertex An Arc GIS Data Modelling GIS Data Modelling

37 Arc-node structure A B C GIS Data Modelling Prof. Qiming Zhou
Arc topology Arc Start Node a1 a2 a3 N1 N2 N3 a4 N4 a5 a6 N6 End Node Left Polygon Right Polygon A B C Arc coordinates Arc Start X, Y a1 a2 a3 40,60 70,50 10,25 a4 a5 a6 55,27 Intermediate X, Y End X, Y 70,60 70,10; 10,10 10,60 30,50 20,27; 30,30; 50,32 55,15; 40,15; 45,27 30,40 Polygon topology Polygon Arcs A B C a1, a5, a3 a2, a5, 0, a6 a6 Outside map Node topology Node Arcs N1 N2 N3 a1, a3, a4 a1, a2, a5 a2, a3, a5 N4 a4 N5 N6 a6 GIS Data Modelling GIS Data Modelling

38 Topological features GIS Data Modelling Prof. Qiming Zhou

39 Network data model GIS Data Modelling Prof. Qiming Zhou

40 TIN data model GIS Data Modelling Prof. Qiming Zhou GIS Data Modelling
1 2 3 6 5 8 7 9 11 10 4 A B C D E F G H I J K L M N EDGES adjacent A B C D E F G H I J K L M N B, K A, C, L B, D C, E, L D, F E, G F, H, M G, I H, J, N I, K A, J, N B, D, M G, L, N I, K, M NODES node# A B C D E F G H I J K L M N 1, 6, 7 1, 7, 8 1, 2, 8 2, 8, 9 2, 3, 9 3, 4, 9 4, 9, 10 4, 5, 10 5, 10, 11 5, 6, 11 6, 7, 11 7, 8, 9 7, 9, 10 7, 10, 11 X-Y Coordinates node# coordinates 1 2 3 11 . . . x1, y1 x2, y2 x3, y3 x11, y11 Z Coordinates node# z_value 1 2 3 11 . . . z1 z2 z3 z11 GIS Data Modelling GIS Data Modelling

41 Creating TIN from contours
Prof. Qiming Zhou Creating TIN from contours GIS Data Modelling GIS Data Modelling

42 Prof. Qiming Zhou TIN surface GIS Data Modelling GIS Data Modelling

43 Object-oriented concepts
Prof. Qiming Zhou Object-oriented concepts An object is a self-contained package of information describing the characteristics and capabilities of an entity under study. In a geographical object data model, the real world is modelled as a collection of objects and relationships between them. Each entity in the GIS is an object. A collection of objects of the same type is called a class. GIS Data Modelling GIS Data Modelling

44 Prof. Qiming Zhou Object data model For GIS purposes it is not sufficient merely to hold data on map elements in the data base. It must also be possible to access the operations to be performed on these elements. An object is an entity that has a state represented by the values of local variables (instance variables) and a set of operations or methods (instance methods). Individual objects belong to a class that defines the type of object. Each class has a superclass from which it can inherit both instance variables and methods. GIS Data Modelling GIS Data Modelling

45 Object data model (cont.)
Prof. Qiming Zhou Object data model (cont.) Polygon object definition Land parcel object definition Superclasses (object) Superclasses (polygon) Class variables Number_of_polygons Instance variables List_of_nodes List_of_arcs Area Value Owner Instance methods Calculate_centroid Draw Overlay Transfer_ownership Re_zone GIS Data Modelling GIS Data Modelling

46 Object data model (cont.)
Prof. Qiming Zhou Object data model (cont.) Object Polygon Land Parcel Polygon-1 Polygon-2 Land parcel-1 Land parcel-2 Land parcel-3 GIS Data Modelling GIS Data Modelling

47 Implementation of O-O model
Prof. Qiming Zhou Implementation of O-O model GIS Data Modelling GIS Data Modelling

48 Three key hallmarks of object orientation
Prof. Qiming Zhou Three key hallmarks of object orientation Polymorphism Encapsulation Inheritance GIS Data Modelling GIS Data Modelling

49 Geospatial database access objects
Prof. Qiming Zhou Polymorphism Application Geospatial database access objects Geospatial database Coverage CAD data Polymorphism Applications Data components Data sources GIS Data Modelling GIS Data Modelling

50 Encapsulation Encapsulation Data set Feature Data set Table
Prof. Qiming Zhou Encapsulation Feature Data set Encapsulation Table Data set Object Class Relationship Class Feature Class GIS Data Modelling GIS Data Modelling

51 Inheritance Inheritance Simple Road Feature Standard feature types
Prof. Qiming Zhou Inheritance Simple Road Feature Inheritance Standard feature types Custom feature types Complex Road Feature Road Feature Road central line Road edge Overpass GIS Data Modelling GIS Data Modelling

52 Prof. Qiming Zhou Advantages The ‘natural’ model: directly corresponds to the object found in reality. Completeness: every object is completely bounded with a defined ‘shell’. Inheritance: a class can include subclasses that can inherit both its data and methods. Openness: allows to modify and expand instance variables and methods. GIS Data Modelling GIS Data Modelling

53 Summary The heart of a GIS is the data model it employs.
Prof. Qiming Zhou Summary The heart of a GIS is the data model it employs. With increasing level of abstraction, models are created from human-oriented conceptual, logical to computer-oriented physical models There is no single type of GIS data model that is best for everything. Commonly used data models include: CAD, graphical and image data models Raster data model Vector data model Object-oriented data model GIS Data Modelling GIS Data Modelling


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