Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition

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 ...