Centre to centre everywhere in the world I've flown, but this is JAR-land now. Could arbitrarily be anything: "All tracks to be measured commencing from a point 2.37km to the SSW of the upper right hand corner of the airport boundary (as defined when chart North is oriented 15 deg to the E of True North), provided the destination lies not less than the specified minimum distance.
NOTE: Different requirements apply if the destination lies closer than the specified minimum distance. Consult JAR 84.87.a.ii.(b).(7) sub-section 987.98.a(2)f."