A world file is a text file that is distributed with many raster datasets. It contains six lines of instructions which describe the location, scale, and rotation of the raster image. ArcGIS can read display information from the world file – but by default, it does not. Instead, ArcGIS prefers to read this information from the raster’s spatial header, if it exists. Many of the common raster formats, including as TIFF and IMG, have spatial headers, making the world file redundant.
If you really, really want to, you can force ArcGIS to always use the world file, if it is available. You may wish to do this because you want to standardize the spatial data associated with each raster, regardless of format. A text file is easier to standardize than the spatial headers of disparate image types. However, you have to be careful about this, because the world file and the spatial header info are not always the same. Choosing to favor the world file could change the spatial properties of your archive data.
In ArcGIS 10, all you have to do to favor the world file is tick a checkbox in the ArcMap (or ArcCatalog) options. It’s a bit trickier in ArcGIS 9.x. You have to enter the Windows registry and search for the correct key. For Windows XP Professional SP3, the key is located at:
HKEY_LOCAL_MACHINE\SOFTWARE\ESRI\Raster\Preferences\filepref.favor_world_file
The default value for this key is false. Setting it to true will force ArcGIS to favor the world file. Double-click the key to change its value.
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