An explanatory list of these codes and other descriptive conventions is provided below.
Date is derived from information on the map.
The record group number assigned to state agencies is sometimes used in this field. For instance the number 017.8 refers to maps in Texas Planning Board records, series 8. If the records or papers are unprocessed, a series designation is not given. An accesion number is assigned when the map is received and is used as a control number.