To Mosaic or not to Mosaic?

Blog Post created by geonetadmin on Nov 20, 2009

Hi, my name is Jeff, and I am a member of the Geodata Raster team at the Eastern ESRI Support Services located in Charlotte, NC. I posed the question above because whether to mosaic or not is one of the most common workflow questions when dealing with rasters. There are many raster formats and depending on the format and the ultimate data product, the answer may change. Some immediate questions to ask are:

    1. Am I looking to create a backdrop for a map or provide imagery capable of being analyzed?

    1. Are the rasters highly compressed, for example .sid or .ecw?

  1. Is file storage a concern for the mosaic? How much room do I have for the mosaic?

There are many more specific questions to consider, but these general questions can prevent future headaches when determining if creating a mosaic is the best course of action.

The mosaic process can create one file that contains several other rasters, but the creation of it can be time consuming and problematic. Plus, there are plenty of other situations where an unmanaged raster catalog may provide the functionality you desire without changing the format or creating a new file.

If you are looking for the ease of adding one file to a map document rather than multiple files or are looking to maintain the format of your compressed raster data, then an unmanaged raster catalog may be the answer. The unmanaged raster catalog resides in a geodatabase and will maintain the extents of all of the rasters added to it, but will not import the rasters. They will maintain the format and then can be added all at once to a map document by simply adding the raster catalog. The unmanaged raster catalog will maintain the location of the original file. This workflow can be particularly handy if you have a large number of SID files that have a file size of 1 gig but an uncompressed size of 20 gigs. A mosaic of several SID files would be considerably large, but the unmanaged raster catalog can utilize the files as they are and load them together at once.

The creation of an unmanaged raster catalog is much quicker than creating a mosaic and can be a great way to display a large number of rasters.

While unmanaged raster catalogs cannot be used for analysis in many of the geoprocessing tools, they can be used for digitizing and backdrops for many different maps.

Below are a few Web Help documents that pertain to this discussion:

 Creating a Raster CatalogMosaicking Raster DatasetsExploring Geodatabase Raster Catalogs


- Jeff S., Support Analyst, Geodata Raster team, ESRI Support Services