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Shapefiles, Topology, and the Geodatabase

Shapefiles, Topology, and the Geodatabase. Longley et al., ch. 9 Zeiler, chs. 4 and 5. Shapefiles and Topology. discrete view separate, countable exhaust the space? space between objects? editing a polygon boundary?. ArcInfo Coverage. ArcView Shapefile. “Limited” Topology.

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Shapefiles, Topology, and the Geodatabase

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  1. Shapefiles, Topology, and the Geodatabase Longley et al., ch. 9 Zeiler, chs. 4 and 5

  2. Shapefiles and Topology • discrete view • separate, countable • exhaust the space? • space between objects? • editing a polygon boundary?

  3. ArcInfo Coverage

  4. ArcView Shapefile

  5. “Limited” Topology • adjacency, connectivity (defined in coverages) • FNODE, TNODE • LPOLY#, RPOLY# • properties that are preserved under stretching of the space • distinction between point, line, area is topological • can't make a line into an area

  6. Adding a New Polygon w/in a Coverage

  7. Shapefiles • “Limited topology” - 6 kinds of shapefiles • Point • Multipoint (several pts. represent one feature) • polyline • multipart polyline (segments disconnected) • Polygon • Multipart polygon • Attributes in separate dBASE tables • no topological info.

  8. Object-Oriented Data Modeling • Objects in the real world • Natural rules and relationships • Rivers flow downstream • Roads handle levels of traffic • Land parcels respect landuse laws • How to build this intelligence into data structures?

  9. OO Principles • things in the world are instances of classes • John Smith - human being • Harrison Blvd. - street • Corvallis - city • Mary’s Peak - mountain (Hugh Grant’s hill??) • Identity, Inheritance, Encapsulation

  10. OO Principles ( cont. )Identity • classes form hierarchies • John Smith is an instance of the class male human beings • male human beings are a subclass of human beings • human beings are a subclass of mammals • mammals are a subclass of fauna • each subclass shares the properties of the class • and may add special properties

  11. OO Principles ( cont. )Identity • geographic objects often group into complex objects • an airport is composed of runways, hangars, terminals • a state is composed of counties • an area coverage is composed of polygons, arcs, nodes

  12. OO Principles ( cont. ):Inheritance • Object can inherit properites • old hierarchical database concept • objects can inherit properties that are true of all objects of that type • e.g., for all polygons • new county in Oregon, still can’t pump gas there • and can also add new properties • e.g., properties true only of a certain class • rural county, always has diesel gas

  13. OO Principles ( cont. ):Encapsulation ( Behavior ) • Object can encapsulate behavior (functions) • what kinds of behavior? • editing rules • e.g, corners of a building must be square • might apply to all buildings but not all polygons • might apply only to some buildings • two adjacent objects must have the same common boundary

  14. Behavior ( cont. ) • attribute rules • e.g., range of possible numbers • dates in numerical format (only 1 to 12) • split and merge rules • 1 feature split or 2 features merged, what happens to attributes? • e.g., split a street, the lengths of two parts are shares of the total • e.g., merge two polygons, their population counts are summed for the combined polygon • e.g., merge two polygons, their population densities are averaged, weighted by area

  15. Example Merge Rule

  16. Behavior ( cont. ) • editing, attribute, split and merge rules • special procedures • e.g., procedure to measure areas of polygons • associated with polygon object type • e.g., procedure to annotate contours • specific interaction rules between objects • e.g., a liquor store cannot be within 500 m of a school • an offramp is required if a street and a freeway intersect • at least one stream must flow out of every stream junction

  17. Encapsulation • things in the world are instances of classes • John Smith - human being • Harrison Blvd. - street • Corvallis - city • Mary’s Peak - mountain (Hugh Grant’s hill??) • instances of a class must share ... • same topological dimensions • same attributes • same behaviors

  18. A “Smarter” Data Model • ArcInfo 7 coverage • geometric information not stored in database • ArcInfo 8 geodatabase • stores geometric information as "shape" attribute • closer to how we actually think about geographic features • e.g., we don't naturally think about an area coverage as a collection of arcs • Identity, Inheritance, Encapsulation (Behavior)

  19. ArcInfo 8 and Microsoft COM • 2,000 reusable software objects • Programmable in Visual Basic for Applications (VBA) • Visual language for representing a data model • Data modeling with Unified Modeling Language (UML)

  20. Microsoft COM( Component Object Model ) • Microsoft standard for re-usable software components • Build software from parts, not from scratch • Makes software easier to write and reuse • Provides widest choice in services, tools, languages, and applications • Controls, tools, and server components • Geographic objects and software objects • e.g., ArcInfo and Excel

  21. Windows Platform Multiple Languages/Tools Componentdeveloper Webprofessional Commercial professional developer Generalpurpose SoftQuad HotMetal Pro Borland Delphi Borland Latte Adobe PageMaker Borland Intrabuilder PowerSoft PowerBuilder Macromedia Director NetObjects Fusion PowerSoft NetImpact VISIO

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