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Best practices for GetCategories API call
All metadata calls and GetCategories in particular, have a significantly large response size when retrieved in full. Here are some suggestions to optimize the usage and increase the efficiency of your application:
Sample GetCategories XML request to get the hierarchy for a top level category:
<?xml version="1.0" encoding="utf-8"?>
If you already have items listed with an old category, and if there is a change, where category is mapped to new CategoryID, a quick way to find the mappings is to call GetCategoryMappings.