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Understanding Vector Data Models in Geographic Information Systems

This resource explores the intricacies of vector data models used in Geographic Information Systems (GIS), focusing on spaghetti and topological models. It discusses how vector data structures explicitly represent spatial locations through points, lines, and areas but imply relationships among them. Furthermore, it examines practical applications, such as the TIGER and GBF/DIME models, along with the evolution of hybrid systems that integrate graphic data structures with database management systems (DBMS). This knowledge is essential for efficient spatial representation and analysis in GIS.

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Understanding Vector Data Models in Geographic Information Systems

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  1. GIS Data Models III GEOG 370 Instructor: Christine Erlien

  2. Representing Geographic Space: Vector Data Structures • Represent spatial locations explicitly • Relationships between entities implicit • Space between geographic entities not stored

  3. Vector Data Models • Multiple data models • Examination of relationships • Between variables in 1 map • Among variables in multiple maps • Data models • Spaghetti models • Topological models • Vector chain codes

  4. Vector Data Model: Spaghetti • Simplest data structure • One-to-one translation of graphical image • Doesn’t record topology  relationships implied rather than encoded • Each entity is a single piece of spaghetti Point Line Area very short longer collection of line segments • Each entity is a single record, coded as variable-length strings of (X,Y) coordinate pairs • Boundaries shared by two polygons  stored twice

  5. Vector Data Model: Spaghetti From Fundamentals of Geographic Information Systems, Demers (2005)

  6. Vector Data Model: Spaghetti • Measurement & analysis difficult • All relationships among objects must be calculated independently • Relatively efficient for cartographic display • CAC • Plotting: fast www.gis.niu.edu/Cart_Lab_03.htm

  7. Vector Data Model: Topological • Topology: Spatial relationships between points, lines & polygons • Topological models record adjacency information into data structure • Line segments have beginning & ending • Link: Line segment • Node: Point that links two or more lines • Identifies that point as the beginning or ending of line • Left & right polygons stored explicitly

  8. Vector Data Model: Topological From An Introduction to Geographic Information Systems, Heywood et al. (2002)

  9. Topological Data Models • Multiple models • GBF/DIME (geographic base file/dual independent map encoding) • TIGER (topologically integrated geographic encoding and reference system) • POLYVRT (POLYgon conVERTer)

  10. Topological Data Models: GBF/DIME • Created by U.S. Census Bureau • Both street addresses & UTM coordinates defined for each link • Topology + direction • Left/right • From/to From Fundamentals of Geographic Information Systems, Demers (2005)

  11. Topological Data Models: TIGER Point Area • Designed for use with the 1990 U.S. Census • Block-level maps • Points, lines & areas explicitly addressed • Census blocks can be retrieved directly by block number Coordinates Line From Fundamentals of Geographic Information Systems, Demers (2005)

  12. Topological Data Models: POLYVRT Entities stored separately but linked to one another through pointers Chains: Collections of line segments with directional information (from-to, left/right) From Fundamentals of Geographic Information Systems, Demers (2005)

  13. ArcGIS/Arcview’s shapefile Shapefile Comprised of 3 file types *.shp contains coordinates *.shx is an index file *.dbf is an attribute file in dbase format Where is topology? Not explicitly stored Created on-the-fly Shapefile  in-between spaghetti & topological data structures

  14. Compacting Vector Data Models • Compact data to reduce storage • Freeman-Hoffman chain codes • Each line segment • Directional vector • Length • Non-topological • Analytically limited  limits usefulness to storage, retrieval, output functions • Good for distance & shape calculations, plotting

  15. Vector Model to Represent Surfaces: TIN TIN allows us to record topographic data as points in a regular or irregular grid.

  16. Vector Model to Represent Surfaces: TIN From Geographic Information Systems & Science, Longley et al. (2005)

  17. Vector GIS: Hybrid & Integrated Systems • Hybrid system • Links graphic data structures with DBMS • Efficiently manage both graphics & attribute data • Allows raster & vector data types From Fundamentals of Geographic Information Systems, Demers (2005)

  18. Vector GIS: Hybrid & Integrated Systems • Integrated system • Entities’ coordinate data stored as relational table • Topological data stored as separate table in same database • Attributes can be • Stored in same tables as graphic entities • Stored as separate tables & linked relationally • GIS more closely integrated with DBMS than in hybrid system

  19. Vector GIS: Object-Oriented Database Management Systems • Emerging as an alternative to hybrid or integrated models • Extends the integrated model by incorporating a spatial query language • Objects inherit properties from the class of objects that they belong to • Variable types & operations particular to that class • Example: ArcGIS’ geodatabase • Shift from previous hybrid orientation

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