The geodatabase is a collection of geographic datasets and capabilities.
The concepts in the following sections will help provide a foundation for learning about and effectively using geodatabases for your GIS work.
Fundamental datasets in the geodatabase
Datasets are the primary mechanism to provide access to geographic information in ArcGIS. The geodatabase contains the following primary dataset types:
Creating a collection of these dataset types is the first step in designing and building a geodatabase. Once you create these, you can add to or extend your geodatabases with more advanced capabilities (such as by adding topologies, networks, or subtypes) to model GIS behavior, maintain data integrity, and work with an important set of spatial relationships.
Geodatabase storage in tables and files
Geodatabase storage includes both the schema and rule base for each geographic dataset plus simple, tabular storage of the spatial and attribute data. All three primary datasets in the geodatabase (feature classes, attribute tables, and raster datasets), as well as other geodatabase elements, are stored using tables. The spatial representations in geographic datasets are stored as either vector features or rasters. These geometries are stored and managed in attribute columns along with traditional tabular attribute fields.
A feature class is stored as a table. Each row represents one feature. In the polygon feature class table below, the Shape column holds the polygon geometry for each feature. The value Polygon is used to specify that the field contains the coordinates and geometry that define one polygon in each row.
A key geodatabase strategy is to leverage the database management system to scale GIS datasets to extremely large sizes and numbers of users (for example, to support simple small databases for one or a few users up to instances with hundreds of millions of features and thousands of simultaneous users). Tables provide the primary storage mechanism for geographic datasets. SQL is very strong at querying and set processing of rows in tables, and the geodatabase strategy is designed to leverage these capabilities.
The geodatabase supports SQL access to feature geometry in the following databases:
- IBM Db2
- IBM Informix
- Microsoft SQL Server
Advanced geographic data types extend feature classes, rasters, and attribute tables
Various geodatabase elements are used to extend simple tables, features, and rasters to model spatial relationships, add rich behavior, improve data integrity, and extend the geodatabase's capabilities for data management.
The geodatabase schema includes the definitions, integrity rules, and behavior for each of these extended capabilities. These include properties for coordinate systems, coordinate resolution, feature classes, topologies, networks, raster catalogs, relationships, and domains. This schema information persists in a collection of geodatabase meta tables. These tables define the integrity and behavior of the geographic information.
As necessary, you can extend your data to support certain essential capabilities. The geodatabase has a number of additional data elements and dataset types that can be used to extend this fundamental collection of datasets.
Transactions and versions in enterprise geodatabases
In addition to advanced geographic data types and functionality such as annotation, topology, networks, and terrains—all of which work on large, high-performance databases—enterprise geodatabases also support the following data management workflows and operations:
- Versioning, which supports multiple simultaneous editors that do not overwrite or block one another.
- The ability to check out and check in updates between geodatabases, and synchronize multiple replicated geodatabases by sharing change-only updates between replicas that can be in any number of database types and need not be connected.
- Create, manage, and use historical archives (for example, analyze and compare the state of a parcel layer over time).
For an overview of enterprise and other geodatabases, see Types of geodatabases.