no graphic objects, then a minimum of two files is needed: *.TAB and *.DAT. While a data set is being edited by a user, temporary files are created by MapInfo Professional. The presence of any of these files locks the data set and prevents it from being edited by any other users. When the changes are saved, the temporary files are deleted by the software. In certain situations such as a power failure while editing is in progress, the temporary files may not be deleted and the changes will be lost. In this case the files should be manually deleted. Normal temporary files have the following file name extensions: .TDA Temporary database file .TIN Temporary index file .TMA Temporary Map File When using a database table such as Oracle Locator or Spatial, if the data is downloaded to the local machine, the temporary file name extensions are: .LDA Local Temporary database file .LIN Local Temporary index file .LMA Local Temporary Map File MapInfo Professional can also use raster images and grid surfaces as layers in a map. These are stored in their native file formats, such as *.JPG, *.TIF or *.PNG, and the software again creates a *.TAB file for each one which includes georeferencing information. A seamless table enables a single layer in a map to be derived from multiple base data sets, such as a mosaic of raster image tiles. When MapInfo Professional creates a seamless table it makes a simple vector layer which contains a rectangle for each base data set with attribute data defining the file path to the files containing the base data. When the seamless table is opened, metadata in its *.TAB file causes the map to display not the rectangles but the contents of the base tables in their place. See also MapInfo Interchange Format MIF and MID External links MITAB - MapInfo .TAB Read/Write Library MapInfo Dataset Format Library of Congress GIS vector file formats