ArcGIS offers two methods for mosaicking raster data, either as a virtual mosaic using a mosaic dataset, or by permanently appending (mosaicking) raster datasets together. A mosaic dataset is a data model within the geodatabase. It creates a mosaicked image on-the-fly according to the mosaicking rules defined within its properties.
Learn more about the mosaic dataset
There are some cases where you may prefer to generate a permanently mosaicked raster dataset. For example:
- You need to provide a single image file to another user or customer who does not support a mosaic dataset.
- Another user or customer is using an older version of the software and cannot connect to a mosaic dataset.
- Your customer requests a single image.
- You want to store your raster data using the least amount of storage space and are not concerned with maintaining overlapping data or individual metadata information for all raster datasets.
There are several geoprocessing tools available for mosaicking multiple raster datasets into a single raster dataset. These are
- Mosaic To New Raster—Mosaics multiple raster datasets into a new raster dataset.
- Mosaic—Mosaics multiple input rasters into an existing raster dataset.
- Workspace To Raster Dataset—Mosaics all the raster datasets stored within the specified workspace into one raster dataset. This is recommended for mosaicking hundreds of raster datasets to a raster dataset stored in a file or ArcSDE geodatabase.
- Raster Catalog To Raster Dataset—Mosaics the contents of a raster catalog into a new raster dataset. This tool is faster than the Mosaic To New Raster tool.
When you right-click a raster dataset in ArcCatalog or the Catalog window and choose the option to load data, you access the Mosaic tool. If you want to mosaic raster datasets to a new raster dataset, use the Mosaic To New Raster tool. You can only mosaic to a raster format that ArcGIS can export. For more information about which formats ArcGIS can export, see Supported raster dataset file formats.
In ArcMap, you can click a raster catalog layer in the table of contents and click Data > Mosaic Raster Catalog to open the Mosaic Raster Catalog dialog box. This allows you to create a mosaicked raster dataset from a selected set of rasters, clipped to the data frame or graphic, or a mosaic of the entire raster dataset. You can optionally apply any color correction settings made on the Layer Properties dialog box. You can also use the Mosaic button 
on the Image Analysis window to mosaic a selected set of raster layers together. They are added to the table of contents as a temporary layer. You have to save this layer as a permanent raster dataset to preserve the mosaic. You can do this by right-clicking the layer in the table of contents and clicking Data > Export Data, or by selecting the layer in the Image Analysis window and clicking the Export button 
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You can export a mosaic dataset to a mosaicked raster dataset using the Copy Raster tool.