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:
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 ...