20230508 14522200 1.0 TRUE US National Grid 100m This layer represents a United States National Grid (USNG) for those portions of Florida falling within Marion County. The USNG is an alpha-numeric reference system based on the UTM coordinate system and is similar to the Military Grid Reference System. Use of the USNG ensures a uniform grid mapping and positional reporting system for search and rescue, emergency planning, response, and recovery.