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Geographical Information Systems and Science Longley P A, Goodchild M F, Maguire D J, Rhind D W (2001) John Wiley and Sons Ltd 9. Geographic Data Modeling © John Wiley & Sons Ltd

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Outline Definitions Data models / modeling GIS data models Topology Example Water facilities

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Definitions Data model set of constructs for representing objects and processes in the digital environment Representation Focus on conceptual and scientific issues

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Role of Data Modeling Real World People Interpretation and Explanation Operational GIS Analysis and Presentation GIS Data Model Description and Representation Line Building Pump House House Street Water Line Water Line Feature Polygon

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Data Model Levels Increasing Abstraction Reality Conceptual Model Logical Model Physical Model Human- oriented Computer- oriented

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Real World Objects and relationships Database Schema (Object state) Physical Model Modeling Process Conceptual Model Lists, flow diagrams, etc Logical Model Diagram in CASE Tool

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GIS Data Models & Applications CAD Graphical Image Raster/Grid TIN Geo-relational Object Engineering design Simple mapping Image processing and analysis Spatial analysis / modeling Surface /terrain analysis / modeling Geoprocessing geometric features Features with behavior

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Raster and Vector Models Raster – implementation of field conceptual model Array of cells used to represent objects Useful as background maps and for spatial analysis Vector – implementation of discrete object conceptual model Point, line and polygon representations Widely used in cartography, and network analysis

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Raster – Satellite Imagery

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Vector - Land Records GIS Survey 9 / / // / / 30.5’26.23’ 20.37’26.23’ 45.81’ 35.44’ R 10’ Survey point Computation Link Surveyed feature

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Topology Science and mathematics of geometric relationships Simple features + topological rules Connectivity Adjacency Shared nodes / edges Topology uses Data validation Spatial analysis (e.g. network tracing, polygon adjacency)

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Polygon Topology Model

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Polygon Topology Contiguity

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Geo-relational Model

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Triangular Irregular Network

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Example Water Facilities Data Model Start with objects and relationships Model as object types and relationships Topological network Hierarchical ‘type of’ Collection ‘composed of’ Add related attribute tables

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House Pump House Pump Meter Valve Hydrant Fitting Main Street Lateral Water Facility Data Types

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Pump Meter Valve Hydrant Fitting Main Lateral Topological Network Model

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Object FeatureEquipmentOperationsRecord PolygonLineNode Building Pump HouseHouse StreetWaterLine MainLateral WaterFacility ValveFittingHydrantMeterPump Network Composed Type Relationship Network Landbase Water Facility Object Model

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Visio CASE Tool (UML Representation)

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Common Mistakes Design in abstract without reference to GIS software core data model Don’t budget right amount of time Too much, too little Try to be too wide ranging and generic instead of specific and practical Design for elegance instead of performance

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Conclusions Data modeling is an art and a science Can’t really understand it without practical experience Mature tools available to help CASE, UML Never forget its GIS data modeling

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