Many to one relationship with the MapCat table. Contains one record for EACH 4th-level Hydrologic Unit Code represented on the image for drainage specific images ONLY.
| Field Name | Field Description | Data Type | Field Size* | MapID | The map or image ID, foreign key to table MapCat | int | 4 | HUC | The USGS hydrologic unit code. Cross reference to HUC table. | char | 8 | RankID | The rank describing the geographic scope of Map relative to the HUC. | tinyint | 1 |
*The text datatype pre-allocates only 16 bytes. Size represents actual bytes for all other data types.