How many checkpoints does ASPRS Edition 2 ask for?
At least 30. ASPRS Edition 2 says accuracy testing should use no fewer than 30 checkpoints, and for projects up to 1,000 square kilometres it recommends exactly 30 (ASPRS 7.14, Table C.1). Larger projects get 10 more for each extra 1,000 square kilometres, up to 120.
How does the number grow with the size of the project?
Up to 1,000 square kilometres, which is far bigger than any single drone site, the recommendation is 30. Above that it rises by 10 for each started 1,000 square kilometres and stops at 120 for projects over 9,000 square kilometres. A 1,500 square kilometre project needs 40, for example, and a 4,200 square kilometre project needs 70.
What if the site is too small for 30 checkpoints?
ASPRS says 30 may not be practical on a very small project. You can then use fewer if the accuracy report says so (ASPRS 7.16.1). The planner keeps checkpoints at least a tenth of the site diagonal apart, a guideline from the US National Standard for Spatial Data Accuracy, but never more than a fifth of the GCP spacing. If 30 will not fit at that spacing, the planner places fewer rather than crowd them together. It then tells you the report needs the reduced-checkpoint statement.
Do I need extra checkpoints for heights under vegetation?
The 30 checkpoints test height on open, bare or hard ground, which ASPRS calls NVA. If your project must also report height accuracy under vegetation (VVA), ASPRS advises another 30, spread across the vegetated areas (ASPRS C.3). The planner cannot place those yet because it does not know where the vegetation is. See the difference between GCPs and checkpoints for why checkpoints are kept separate from the control points.
References
American Society for Photogrammetry and Remote Sensing (2024) ASPRS Positional Accuracy Standards for Digital Geospatial Data, Edition 2, Version 2. Available at: https://publicdocuments.asprs.org/PositionalAccuracyStd-Ed2-V2 (Accessed: 7 October 2026). doi: 10.14358/ASPRS.PAS.2024
Federal Geographic Data Committee (1998) Geospatial Positioning Accuracy Standards, Part 3: National Standard for Spatial Data Accuracy. FGDC-STD-007.3-1998. Available at: https://www.fgdc.gov/standards/projects/accuracy/part3/chapter3 (Accessed: 6 October 2026).
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