The geodatabase

The geodatabase is a vector data format introduced by ESRI with ArcGIS® software. In technical terms, the geodatabase is a relational database, a type of database composed of various tables that organize data and are linked to one another.

It may be more helpful at this point, however, to just think of a geodatabase as a container for storing geographic data. The geographic data stored in a geodatabase may be point, line, or polygon feature classes as well as other collections of data described below. The geodatabase has many powerful capabilities for modeling real-world objects—you will learn more about it later in this module.

How a geodatabase organizes data

In addition to point, line, and polygon feature classes, a geodatabase can store annotation feature classes. Annotation is descriptive text about features or areas on a map.

In the geodatabase, feature classes can be standalone or they can be organized into larger units called feature datasets. A feature dataset stores feature classes that have the same coordinate system and the same spatial extent, meaning they occupy the same geographic area. While all features in a feature class must have the same geometry type, the same is not true for feature datasets. Feature datasets can store feature classes with different geometry types.

Feature classes grouped into a feature dataset normally have some kind of spatial relationship to one another. For example, they might be adjacent, intersect each other, or coincide with each other.

Feature class tables store feature geometry and attribute information. Some attributes in the feature class tables are automatically created and maintained by the geodatabase. For line feature classes, the geodatabase automatically calculates the length of each feature and stores that data in a field called Shape_Length. For polygon feature classes, the geodatabase calculates the perimeter and area of each feature and stores those values in fields called Shape_Length and Shape_Area, respectively.

Sometimes, for database efficiency (to speed up data queries and feature draw time), feature attributes may be stored outside the feature class table in a separate table. Geodatabase tables that contain only feature attributes—no geometry—are called nonspatial tables.

A geodatabase can contain standalone feature classes, feature classes grouped into feature datasets, annotation feature classes, and nonspatial tables.