Data on this portal is grouped into three Tiers: A, B, and C. These tiers are based on CO-OPS specifications.
- Accuracy: 10 cm or better
- Vertical Control: 5 or more benchmarks, annual leveling, 2nd Order Class 1 or better
- Accuracy: 30 cm or better
- Vertical Control: 3 or more benchmarks with 3rd Order biennial level OR ellipsoidal referenced via GPS
- Accuracy: greater than 30 cm or unknown
- Vertical Control: not required
If no Tier is listed, or if the sensor standards are unknown, the data will be assigned Tier C.