Class 4 Notes Continued

1. Define the geodatabase.
The geodatabase (or geographic database) is similar to the ESRI coverage data model as a container in which to store data. They are three types of geodatabases used in ESRI products that can be selected for a varying data requirements. ArcGIS sotware is based around the concept of a geodatabease. The geodatabase is a more powerful data model than other alternatives offered by ESRI and allows users to form complex relationships between data as well as providing tools to streamline data entry and query construction.

2. List the elements of the geodatabase.
Some of the elements of the geodatabase include (as per the ESRI documentation)

• Annotation - A specialized feature class that stores text or graphics that provide information about features or general areas of a map. An annotation feature class may be linked to another feature class so that edits to the features are reflected in the corresponding annotation (i.e., feature-linked annotation).
• Cadastral Fabric - A cadastral fabric is a seamless parcel boundary network, which is created and maintained using data from survey records.
• Dimension - A special type of geodatabase annotation that shows specific lengths or distances on a map. A dimension feature may indicate the length of a side of a building or land parcel, or it may indicate the distance between two features such as a fire hydrant and the corner of a building.
• Feature Class - A collection of geographic features with the same geometry type (i.e., point, line, or polygon), the same attributes, and the same spatial reference. They allow homogeneous features to be grouped into a single unit for data storage purposes; for example, a feature class of city streets.
• Feature Dataset - A collection of feature classes stored together that share the same spatial reference. Feature classes in a feature dataset share a coordinate system, and their features fall within a common geographic area. Feature datasets are used to help model spatial relationships between feature classes.
• Geometric Network - Edge and junction features that represent a directed-flow system network, such as a utility or hydrologic system, in which the connectivity of features is based on their geometric coincidence.
• Network Dataset - A collection of topologically connected network elements (e.g., edges, junctions, and turns) that are derived from network sources, typically used to represent an undirected-flow system network such as a road or subway system.
• Raster Catalog- A collection of raster datasets defined in a table of any format, in which the records define the individual raster datasets that are included in the catalog. Raster catalogs can be used to display adjacent or overlapping raster datasets without having to mosaic them together in one large file.
• Raster Dataset - Any valid raster format organized into one or more bands. Each band consists of an array of pixels (cells), and each pixel has a value (e.g., a Landsat satellite image).
• Relationship Class - A class similar to relationships that exist within an RDBMS. Relationship classes manage the associations between objects in one class (e.g., table or feature class) and objects in another. Objects at either end of the relationship can be features with geometry or records in a table.
• Schematic Dataset - A dataset used for graphically representing network connectivity and sets of relationships.
• Survey Dataset - An integrated collection of specialized survey feature classes and associated survey measurements.
• Table - A set of data elements arranged in rows and columns. Each row represents a single record. Each column represents a field of the record. Tables typically store stand-alone attribute information or information associated with a spatial location such as addresses.
• Terrain - A triangulated irregular network (TIN)-based dataset that uses feature classes as data sources to model multiple resolution surfaces using z-values.
• Toolbox - A collection of dataflow and workflow processes for performing data management, analysis, and modeling.
• Topology - The arrangement that constrains how point, line, and polygon features share geometry within a geodatabase. For example, street centerlines and census blocks share geometry, and adjacent soil polygons share geometry. Topology defines and enforces data integrity rules, topological relationship queries and navigation, and sophisticated editing tools. It also allows feature construction from unstructured geometry.

3. Describe how the geodatabase is different that other spatial data formats in it's handling of 'real-world' behaviors.
The geodatabase implements several data integrity validation tools that allows the users to enforce 'real-world' behavior patterns through pre-defined 'templates'. Unlike ESRI's other available data formats 'real-world' behavior is enforced by limiting the range of potential user inputs through subtypes, domains, and default values to feature classes.

4. Describe the types of geodatabases available at 9.2.
ArcDesktop 9.2 uses three types of geodatabases, the personal, the file, and the ArcSDE geodatabase. The personal geodatabase is based on the MS Access relational database model and is limited to 2 GB of data. It is not very robust and is limited in its multiuser editing capabilities. The file geodatabase is based on a SQL relational database model and can handle up to 1 TB of data. It requires no additional software other than the ArcDesktop program. In this type of geodatabase each data set is stored in a separate file as opposed to the personal geodatabase which stores all datasets in a single *.mdb file. The file geodatabase is the recommended native format for ArcGIS. The ArcSDE geodatabase requires an additional relational geodatabase software package such as Oracle and SQL server. It is employed for enterprise solutions and its upper limits are dependent on the software package upon which it is based.