datamodel_vector

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  • There are two significant model categories at present:
    Graphic Models: Vector and Raster
    Database Models/Structures: simple lists, sequential files, indexed files, hierarchal files, network files, relational database, etc.
    Today we’ll touch upon real-world entities translated into database objects, but our main focus will be on the models used in representing GIS data graphically (Vector vs Raster)
  • Source: Bernhardsen, Tor. (1999). 2nd Ed. Geographic Information Systems: An Introduction. p 38. Fig 3.1. (simplified model of real world)
    The process of interpreting reality by using both a real world and a data model is called data modeling.
  • Source: Bernhardsen, Tor. (1999). 2nd Ed. Geographic Information Systems: An Introduction. p 39. Fig 3.2. (Modeling process)
    The process of interpreting reality by using both a real world and a data model is called data modeling.
  • datamodel_vector

    1. 1. GIS Data Models
    2. 2. GIS Data Models The real world can only be depicted in a GIS through the use of models that define phenomena in a manner that computer systems can interpret, as well perform meaningful analysis
    3. 3. GIS data models Model Abstraction of realworld/process/phenomenon GIS data model Set of constructs/rules for describing or representing the real world within a computer Two data models Vector Raster
    4. 4. Data Models Vector A coordinate based data structure commonly used to represent geographic features. Homogenous units are points, lines, and polygons. • Mostly used for representing discrete geographical features such as building, wells, roads etc., Raster A cellular based data structure composed of rows and columns for storing images. Homogenous units are called cells or pixels. • Mainly Used for representing continuous surface e.g. soil, elevation, rainfall etc.,
    5. 5. Vector Data Model
    6. 6. Real World > Data Modeling Source: Bernhardsen, Tor. (1999). 2nd Ed. Geographic Information Systems: An Introduction. p 38.
    7. 7. Real World > Modeling Process Source: Bernhardsen, Tor. (1999). 2nd Ed. Geographic Information Systems: An Introduction. p 39. Fig 3.2.
    8. 8. Vector Data Model Points Points are associated with single set of coordinates (X, Y) Lines Lines are a connected sequence of coordinate pairs Polygons Areas are a sequence of interconnected lines whose 1st & last coordinate points are the same
    9. 9. Scale Scale plays a major role in how you represent a spatial entity i.e whether to represent an entity as a point, line or a polygon Scale = Map Distance / Real Distance E.g. 1: 1,000: large scale 1:1,000,000: small scale
    10. 10. Vector Data Formats Shapefile (ArcView/ArcGIS; ESRI) ArcInfo Coverage Digital Line Graph (DLG) Others: HPGL, PostScript/ASCII, CAD/.dxf
    11. 11. Your will encounter mostly Arcview shape files or ArcInfo Coverage CAD/.dxf Conversion tools are available in most GIS platforms However, topology should be built to make it useful for further analysis

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