What exactly is a geodatabase?

A geodatabase is a relational database that stores geographic data.

At its most basic level, the geodatabase is a container for storing spatial and attribute data and the relationships that exist among them. In a geodatabase, which is a vector data format, features and their associated attributes can be structured to work together as an integrated system using rules, relationships, and topological associations. In other words, the geodatabase allows you to model the real world as simply or complexly as your needs dictate.

Geodatabases are created, edited, and managed using the standard menus and tools in ArcCatalog™ and ArcMap™.

The data contained in the SantaBarbara geodatabase (SantaBarbara.mdb) is listed in the ArcCatalog Catalog tree and displayed in ArcMap.

Types of geodatabases

There are two types of geodatabases: personal and enterprise (enterprise geodatabases are sometimes called ArcSDE® geodatabases).

A personal geodatabase has the .mdb file extension (a format used by Microsoft Access) and can be read by multiple people at the same time, but edited by only one person at a time. A personal geodatabase has a maximum size of 2 gigabytes (GB). Vector data is stored in the database, while raster data is referenced.

Personal geodatabases are appropriate for smaller workgroups and for managing small to moderately sized datasets.

Enterprise geodatabases are suitable for large workgroups and enterprise GIS implementations. They can be read and edited by multiple users at the same time, and they can store both vector and raster data.

Enterprise geodatabases require ArcSDE software and a DBMS (database management system) such as IBM DB2, Informix, Oracle, or Microsoft SQL Server. The spatial data is stored in the DBMS and ArcSDE allows you to view and work with the data from your GIS software applications. With some database management systems, you can directly connect to your data from ArcCatalog or ArcMap. For others, ArcSDE must manage the connection.

An enterprise geodatabase stores large spatial datasets using ArcSDE and a commercial database management system. Some database software allows for a direct connection between the ArcGIS application and the database.

If a project becomes too large for a personal geodatabase, you can easily move the data stored in a personal geodatabase to an enterprise geodatabase using ArcCatalog.

Table 1. Comparison of enterprise and personal geodatabases
	DBMS	Client / Server	Long Transactions*	Disconnected Editing	Editors	Raster Data	Size
Enterprise	IBM DB2, Informix, Microsoft SQL Server, Oracle	Yes	Yes	Yes	1 or more at the same time	Stored	Unlimited
Personal	Microsoft Access	No	No	No	1 at a time	Referenced	Up to 2 GB

*Database transactions spanning multiple edit sessions