The main set of around 378 pillars across the country.
Secondary pillars were positioned to fill in the gaps between the primary pillars.
Third order stations filled in the gaps between the second order stations.
Fourth order stations filled in the gaps between the 3rd order stations.
13th Order (GPS)
The marks for GPS Stations, which were marks surveyed by GPS before the Passive Station Database was created, are sometimes referred to as 13th order.