What is an Overlay?

The term Overlay is used to describe a view of a dataset. A dataset can be:

• a read-only graphical file (e.g. an NTF, DXF, or BMP file)
  
  
• a user dataset (BDS file)
  
  
• a database (IDB file)
  
  
• stored within the SIS Workspace Definition (SWD) (internal dataset or index dataset)
  
  
• data retrieved from a spatial database, e.g. Oracle, PostGIS, Microsoft SQL Server 2008.
  
  
• an internal binary geometry dataset

For a full list of datasets which can be included as overlays, see Dataset Formats.

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