Last updated
6/19/02
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ArcGIS Geodatabase: Information
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Introduction
ArcGIS supports a new type of dataformat called the geodatabase.
There are two kinds of geodatabases -- personal and multiuser. The
personal geodatabase can only be edited by one person at a time
and is stored in Microsoft Access format. The multiuser geodatabase can be
edited by many users at the same time and is stored in Oracle,
SQL Server, Informix, or IBM DB2. It also requies ArcSDE for editing.
These geodatabases can be edited in ArcMap/ArcView, ArcEditor, or ArcInfo.
The following table is a brief overview of the geodatabase capabilities
for each module:
| |
ArcView/Map
| ArcEditor
| ArcInfo |
| Read, Display, Query, & Use |
Any geodatabase |
Any geodatabase |
Any geodatabase |
| Editing |
Edit simple personal
geodatabases1
Can edit simple feature classes,
annotation, tables, and simple feature datasets |
Edit all geodatabases
Multiuser geodatabase
editing requires ArcSDETM |
Edit all geodatabases
Multiuser geodatabase
editing requires ArcSDE |
| Schema management and database
design |
Create simple schemas for personal
geodatabases1
Supports: points, lines, polygons,
annotation, and tables
No topology
No geometric
networks
No relationship classes
No feature-linked
annotation
No dimension classes
No raster support
No custom
feature classes
| Create all schemas for any
geodatabase
Multiuser geodatabase support requires ArcSDE |
Create all schemas for any
geodatabase
Multiuser geodatabase support requires
ArcSDE |
| 1 Simple personal geodatabases model
spatial features that are very much like ESRIŽ shapefiles: points,
lines, and polygons without topology. Personal geodatabases also
allow you to store multiple feature classes together in a single
feature dataset, as well as provide annotation
support. |
The ART lab currently does not have any of the database software
required to create a multiuser geodatabase, so these documents will focus
on the personal geodatabase.
Personal Geodatabase
The personal geodatabase can include many types of data, including
coverages, shapefiles, CAD drawings, INFO tables, and DBF tables. It
does not support raster data. Because these datasets will be stored
in the relational database Microsoft Access, they should be arranged into
a logical database architecture (to be designed by you, the user). The
personal geodatabase will be given a name of filename.mdb that is
browsable and editable by the ArcGIS modules, but it can also be opened
with Microsoft Access if you feel the need to see how Access is organizing
your data behind the
scenes. Figure 1 shows what the personal geodatabase can look like in
ArcCatalog. ArcCatalog is the easiest and most straightforward way to
create a personal geodatabase.
Fig. 1. A screenshot of the
personal geodatabase structure in
ArcCatalog. |
Below is a zoom of the ArcCatalog tree view of the personal
geodatabase, srer.mdb. The personal geodatabase can contain the
following items:
Feature Datasets
A feature dataset is equivalent to a directory or folder in a computer
operating system. It is used to help organize the data into a logical
structure. It can contain feature classes and relationship classes, but
not tables.
The feature dataset, even though is is equivalent to a directory, must
have a specified projection that is identical to the projections for the
coverages/shapefiles to be stored inside of it. See the procedures
section for instructions on how to define the coordinate system and import
data.
Feature Classes
The feature class is the coverage, shapefile, or CAD drawing. They can
be stored at the root of the geodatabase or inside of a feature dataset.
Remember that the personal geodatabase does not support
raster data. You can create new feature classes or you can import
coverages/tables/shapefiles as feature classes. You can also create
relationships (called relationship classes, described below) between
feature classes. See the procedures
section for details.
Following is a description from the help documents under "How data is
converted":
The feature class stores both the geometry and attributes from the
input data. The feature class is automatically registered with the
geodatabase system tables so that it can participate in relationships and
geometric networks, have validation rules, and so on. Similarly, when a
table is imported, a table is created in the geodatabase and automatically
registered with the geodatabase system tables. Coverages, shapefiles, and
CAD feature classes are imported into ESRIŽ simple feature classes. INFO
and dBASE tables are imported into ESRI simple row tables.
Any table, shapefile, or coverage that is imported by some other
mechanism will not be registered with the geodatabase system tables and
therefore will not be a true geodatabase feature class or table. The
ArcGIS system has tools to register these feature classes and tables with
the geodatabase.
Tables
Tables can only be stored at the root of the geodatabase. You can store
the following table formats: INFO, dBase, VPF, or OLE DB.
You can create relationships (called relationship classes, described
below) between tables and feature classes.
Relationship Classes
The relationship class is identical to a relate in ArcInfo -- the two
items to be related must have a common attribute (primary and foreign
keys). The related information will show up in ArcMap if you do an
Identify on a feature, and the related data can be edited through
ArcMap, ArcInfo, or ArcEditor. To use the related information for
symbology purposes in ArcMap, you must create a join in ArcMap, but you
will be able to choose the relationship class on which to base the join
instead of defining it again. You can read more about this in the procedures
section.
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