Raster data

How raster data is handled depends on whether you are working with a personal geodatabase or an enterprise geodatabase. In a personal geodatabase, raster data is referenced rather than physically stored. In an enterprise geodatabase, raster data is physically stored just like vector data.

With both personal and enterprise geodatabases, you can view and manage your raster data much as you would vector data.

There are two types of raster objects that you can create in a geodatabase: raster datasets and raster catalogs.

Raster datasets

A raster dataset is created from one or more individual rasters. When creating a raster dataset from multiple rasters, the data is mosaicked, or aggregated, into a single, seamless dataset in which areas of overlap have been removed. The input rasters must be contiguous (adjacent) and have the same properties, including the same coordinate system, cell size, and data format. For each raster dataset, ArcGIS creates an ERDAS IMAGINE file (.img).

Which raster formats are supported?

Among the many raster formats supported by the geodatabase, you can create raster datasets from data stored in the following formats:

· ERDAS IMAGINE

· ESRI GRID

· JPEG

· MrSID

· TIFF

Raster datasets are always managed by the geodatabase. This means that the .img files are stored in a separate folder with the same name as the geodatabase. If the geodatabase is moved to another location, the folder containing the .img files moves with it.

This raster dataset was created from a single satellite image.

Raster catalogs

A raster catalog contains a collection of rasters that can be noncontiguous, stored in different formats, and have other different properties. In order to view all the rasters in the catalog, they must have the same coordinate system and a common geographic extent.

A raster catalog is defined as a table in the geodatabase which you can view like any other table in ArcCatalog. Each raster in the catalog is represented by a row in the table.

You can choose whether or not a raster catalog is managed by the geodatabase. The geodatabase manages a raster catalog similarly to the way it manages a raster dataset (it creates ERDAS IMAGINE files for each input raster and stores them in a folder with the same name as the geodatabase).

If you choose not to have the geodatabase manage the catalog, the location on disk where the rasters are stored will be recorded in the raster catalog table, but if the geodatabase is moved, the raster data will not move with it.

This raster catalog contains four rasters.

Table 2. Comparison of raster datasets and raster catalogs
Raster Dataset	Raster Catalog
Single dataset built from one or more rasters	Collection of rasters
Homogeneous source data: same resolution, format, coordinate system	Heterogeneous source data: different resolutions, formats, data types, file sizes
Faster display	Slower display. The more rasters, the slower the display
Loss of overlapping pixels when mosaicked	Overlapping pixels are preserved
One metadata file	Metadata files for the catalog and for each raster