If your home is a rectangle, measure the first floor inside/outside length and width of your house. Each measurement is rounded to the nearest foot. Then length times width is your “BASE AREA” shown on the ICS. "UPPER FLOOR AREA" is computed in the same manner. Link to explain "APPENDAGE ADJ". If your calculations are less then shown on your ICS, your taxes will be reduced once this is corrected.
I will refer to the Alabama Appraisal Manual 2005 created by the ADOR, as AAM followed by chapter - page.