The basic network of leveling lines in the City of Los Angeles are the primary lines and they form the boundaries of the adjustment areas. (See map Figure 1) On Primary lines 1st Order Class II observing methods and rejection criteria are followed. For the !980 Adjustment, the primary lines were simultaneously adjusted to fit the 1978 Southern California Re-leveling Program adjusted by the National Geodetic Survey and published on April 2, 1980. Expected accuracy between bench marks on primary lines is ± 2mm square root of (k), where k is the distance between bench marks in kilometers.

The primary lines form a fixed framework for the adjustment of the secondary lines within. On secondary lines, 2nd Order Class II observing methods and rejection criteria are followed except that loop closures are limited to is ± 6mm square root of (k). Expected accuracy between bench marks on secondary lines is ± 4mm square root of (k).

The elevation published in this index is the elevation at the time of observing. Thereafter the stability of the physical mark and crustal movements within the area should be taken into account when checking between bench marks.