ArcGIS Data Models Practical Templates for Implementing GIS Projects

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1 ArcGIS Data Models Practical Templates for Implementing GIS Projects GIS Database Design According to C.J. Date (1995), database design deals with the logical representation of data in a database. The process involves the identification of relations and their attributes. When applied to GIS databases, this is a type of data modeling that is founded on geographic representations of objects, relationships, and behaviors. The process of GIS database design uses schemas to represent data sets, domains, relationships, spatial rules and map layers. ESRI has developed many industry standard data models to assist users in developing GIS projects. These models are built for specific target application domains, where an application domain is the realm or area of use of an application, such as business, health information science, or land parcel management. Most systems are developed to address the requirements of a specific class of applications, and provide features to support these requirements. This criterion specifies the target application domain(s) for each system. Another view would be to say that it involves the subject matter of an application from the perspective of its user organizations. The Role of Thematic Layers Thematic layers form the basis for organizing geographic representations. Most commonly, they are organized as collections of common geographic elements such as soil types or satellite imagery. A transportation network might contain streets, intersections, bridges, and ramps. In practice the identification of thematic layers in a GIS database is influenced by intended use and available data sources. Most graphic representations of GIS data models include, therefore, a listing or representation of the thematic layers to be stored in the database. Designing the Geodatabase In ArcGIS, the design of the geodatabase is based on a schema, and can include the data definitions, integrity rules, and behaviors. It also contains an organized collection of features and themes. The design may address rules and schema properties used to model behaviors. Some of the common elements in the GDB include:

2 Feature Classes Collection of features representing same geographic element Feature Datasets Collection of related feature classes Topologies Shared geometries and integrity Networks Connectivity and flow modeling Raster datasets and catalogs Storage of images Geodatabase elements are organized into parts of schema that includes the data sets (feature class, raster, attribute tables), domains (used to maintain integrity), relationships, and spatial rules (including topologies). Additionally, the schema may include the identification of layers which deals with the symbolization of feature data sets. The design process begins with the identification of the products to be produced. These could include analytical and graphical products used in reports. Next the key thematic layers are identified as to their source, representation, and symbology. Scale ranges and spatial resolutions are specified for the spatial data. If logical groupings are evident, data sets are derived for the feature classes. Tabular data likewise must have structural definitions that include the attributes, ranges, subtypes, and relationships as necessary to model behavior. The spatial properties of all feature data should be defined including the spatial reference, networks, and topologies, if necessary.

3 At this point, the initial attempt at geodatabase design may be facilitated by studying existing GDB models. Frequently, existing application domain models can be modified to meet all or part of the design requirement for the application at hand. Once the model has been developed, the process of implementation and refinement can commence. Often this process includes the development of prototypes that represent a subset of the final form of the GDB. These prototypes are constructed and data is loaded into the structure. This approach allows for review and refinement of discrete aspects of the emerging GDB. In an enterprise environment work flows for construction and maintenance of the database will be considered. This process includes documented practices, standards, and metadata development. In the final phase of the process the design itself is documented through drawings and schema diagrams. This documentation is useful in conveying the structure and function of the GDB to all members of a design team.

4 Using Design Patterns Design patterns are recurring solutions to software design problems that are frequently encountered in application development. Design patterns deal with design and interaction of objects, as well as providing a communication platform concerning elegant, reusable solutions to commonly encountered programming challenges.

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