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.
Quick links to ESRI documentation
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.
