As many of you have probably noticed, the [Additional Properties] section of the .GTM file has an ever growing list of entries that it will support. Some of these entries, such as Custom Attribute Tab definitions, Feature Tooltip definitions, Dynamic Graphics definitions, non-Category Raster definitions, and Custom Raster file definitions, can even dwarf the rest of the .GTM file’s content with their bulk.
Since version 8.0.x.29 of GTViewer, there has been a special entry in the [Additional Properties] section called LoadSupplementalFile. This entry defines a path to a file (which can either be an absolute path or a path relative to the .GTM file). As the .GTM file is processed and a LoadSupplementalFile entry is encounter, the contents of the file it points to will be inserted into the [Additional Properties] section at the entry’s position. Using the LoadSupplementalFile entry has two major benefits: 1) bulky entries like Custom Attribute Tab definitions and Feature Tooltip definitions can be stored in a separate file making a .GTM file without a lot of verbose entries that can logically be grouped together elsewhere, and 2) separating entries like non-Category Raster definition and Custom Raster Definitions into separate files makes them easier to update since the .GTM file itself doesn’t have to be edited when changes are needed.
The Supplemental Files are required when using the .GTM file since they are referenced by the entry, but they are embedded into Extract Files (.GTX) and are, therefore, not needed when using this file type.