Geodatabases

Introduction to Geodatabases

These are notes written by someone learning to use ESRI geodatabases. Specifically, the variation known as the "personal geodatabase" (or PGDB).

Brian Wilson 16:10, 15 January 2006 (PST)

Scope

I am not attempting to duplicate the ESRI documentation. When I learn something new, I write about it to help cement it more firmly in my head, and so that I can refer back to my notes later.

Links to ESRI geodatabase stuff

Datamodels

ArcGIS Desktop documentation The Workbook contains a quickstart guide and exercises. The "Building" book is more complete.

Two main types of ESRI geodatabase

Multiuser Geodatabase -- if you use ArcSDE-based geodatabases, you get version control and multiuser features. ArcSDE is the 'application tier'; a layer of software that contains the geospatial features required to implement a geodatabase on top of various backend databases (Oracle, SQL Server, DB2, etc) which might or might not have any builtin spatial features.

Personal Geodatabase -- based on the MS Access ("Jet") database format; allows many of the same features as SDE for an individual user. No support for multiuser or versioned access. (In fact, I have seen Jet files blown apart if more than one user writes to it... I have heard people claim that multiuser access to Jet files is fine but my own bad experiences belie this.)

Terminology

An informal Comparison of geodata formats

Data model = a template that you can use to build a geodatabase, including documentation and suggested feature classes and topology rules

Feature Dataset = Feature class(es) + topology + network objects

Feature Class = a table containing spatial data + attributes

Table = rows and columns of data; can contain spatial fields

Relationship class = binds tables together; can contain additional data

Topology = rules defining requirements for data to be stored in a dataset

Geometric network = topology rules defining how spatial features are connected

PGDB - you can keep all the data for a project in one PGDB.

Vector data -- Network Survey data

Raster data (ArcGIS 9.0+) --

Raster catalog -- You can have multiple rasters in a feature class, for example to store aerial photos when you don't want to create a mosaic.

Raster time series - you can have multiple rasters in a feature class ordered as layers and sorted by time; you can use the ordering to control how overlapping rasters are layered, too.

Annotation --

Metadata --

Tabular data --

Topology rules --

XML (ArcGIS 9.0+) -- XML can be used to import and export data. The geodatabase XML schema is documented on the ESRI site.

Topology

I am at home right now, where I use ArcView 8.3. ArcView which does not support topologies. I will write more on this topic when I have access to ArcInfo.