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Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition by Michael D. Kennedy

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Geodatabases—Logical Construction

Within the single file of a geodatabase, there is the framework for quite a complex hierarchy of elements. You have had some experience with this hierarchy earlier, but here is a summary, with a bit of additional information. The description is based on the file geodatabase, which resides within a folder. ArcSDE geodatabases look somewhat different, but only at the top levels.

The database may consist of the following:

(A) Freestanding, and not necessarily related:
  • Feature classes, resembling the point, line, and polygon classes you have dealt with
  • Raster datasets, which may represent surfaces (e.g., elevation), areal phenomena (e.g., land cover), or images (e.g., orthophotoquads, scanned maps)
  • Triangulated irregular network (TIN) datasets9
  • Tables, which are referred to as object classes, and which may be imbued with “behavior,” as discussed later in the text.
(B) Feature datasets, whose constituents share a common geographic reference (datum, projection, units, and so on) and that are composed of the following:
  • All the elements cited above in (A)
  • A relationship class that is a set of relationships between the features of two feature classes
  • A geometric network that consists of
    • A junction feature class
    • An edge feature class.

Geometric networks are useful in a variety of areas, such as routing school buses over a road network and keeping track of electrical or piping systems. While I have avoided trying to divide GIS applications into ...

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