The boundary is the extent of all the image datasets, defined by their footprints, in the mosaic dataset. It is a polygon feature class stored in the geodatabase. The boundary is created using the Build Boundary tool or as an option when using the Add Rasters To Mosaic Dataset tool. It is created by merging all image footprints (not including service overviews) into a single or multipart polygon. Once it's created, you can view it in the Contents pane as a layer that is part of the mosaic dataset's expanded view.
The boundary is used to determine the spatial extent of the mosaic dataset. It is not necessary to have a boundary that is a union of all the footprints. The Build Boundary tool allows you to simplify the boundary using a convex hull method or by calculating the envelope of the mosaic dataset. These options are recommended when creating mosaic datasets containing images covering the world's extent or when boundaries have many vertices, such as more than 5,000.
You can clip the mosaic dataset to the boundary; for example, when viewing the mosaic dataset, the mosaicked image is clipped to the boundary feature class. If the mosaic dataset contains image data that extends beyond the boundary, this data is not visible in the mosaicked image. Therefore, if you have image data that extends beyond the area you want displayed in the mosaic dataset, you can limit what is viewable by modifying the boundary.
To clip the mosaic dataset by its boundary, set the Always Clip The Mosaic Dataset To Its Boundary property to Yes on the Mosaic Dataset Properties dialog box.
In the example below, the boundary has been edited. The footprints still represent their full extent; however, the mosaicked image is cropped by the extent of the boundary. There is no loss of image data. If you edit this boundary to extend it outward, the image data that you cannot see will appear. This is because you are not editing the source data—only the boundary of the mosaicked image.
You can edit the boundary using the standard editing tools. You can also replace the boundary file with another polygon feature class using the Import Mosaic Dataset Geometry tool.
The coordinate system for the boundary is defined by the coordinate system of the mosaic dataset.