Baseline

BASELINE – specific survey line on which all latitude measurements are based

Merriam-Webster Online Dictionary
baseline (noun)
1.
a line serving as a basis , especially one of known measure or position used (as in surveying or navigation) to calculate or locate something
2.
a) either of the lines on a field that lead from home plate to first base and third base and are extended into the outfield as foul lines - baseball
b) - base path
3.
a boundary line at either end of a court (as in tennis or basketball)
4.
a usually initial set of critical observations or data used for comparison or a control
5.
a starting point - the baseline of this discussion