We have been supplied a feature class of the geology for our region however the layer file is for the whole country. The issue this creates is that when you display your symbols they display all categories embedded in the layer file. This means many of the geological units which aren't located within the region are displayed in the legend. I can manually remove the empty categories by clicking on the count button in the symbology tab and removing categories with a count of zero but this is only practical for small data sets. Is there a quicker way to show only the units within the region?