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GIS Data Models III GEOG 370 Instructor: Christine Erlien Representing Geographic Space: Vector Data Structures Represent spatial locations explicitly Relationships between entities implicit Space between geographic entities not stored Vector Data Models Multiple data models

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gis data models iii

GIS Data Models III

GEOG 370

Instructor: Christine Erlien

representing geographic space vector data structures
Representing Geographic Space: Vector Data Structures
  • Represent spatial locations explicitly
  • Relationships between entities implicit
    • Space between geographic entities not stored
vector data models
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
vector data model spaghetti
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
vector data model spaghetti5
Vector Data Model: Spaghetti

From Fundamentals of Geographic Information Systems, Demers (2005)

slide6

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

vector data model topological
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
vector data model topological8
Vector Data Model: Topological

From An Introduction to Geographic Information Systems, Heywood et al. (2002)

topological data models
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)
topological data models gbf dime
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)

topological data models tiger
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)

topological data models polyvrt
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)

arcgis arcview s shapefile
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

compacting vector data models
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
vector model to represent surfaces tin
Vector Model to Represent Surfaces: TIN

TIN allows us to record topographic data as points in a regular or irregular grid.

slide16

Vector Model to Represent Surfaces: TIN

From Geographic Information Systems & Science, Longley et al. (2005)

vector gis hybrid integrated systems
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)

vector gis hybrid integrated systems18
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
vector gis object oriented database management systems
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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