Ground Control Density Calculator
Control density and — with a polygon and point list — the actual layout: nearest neighbours, outside points and the exact largest gap.
Inputs
Control density and — with a polygon and point list — the actual layout: nearest neighbours, outliers and the exact largest gap.
Enter the values and press Calculate.
Or load an example to see a worked result.
Density alone draws no layout: the same count can be spread evenly or bunched in one corner. Choose the point-layout review to see the distribution and the largest gap.
Batch from CSV
One row per calculation, with a header row. Values use the units currently selected in the form above. Up to 10,000 rows; nothing is uploaded.
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Quick review: enter the area, control count and (separately) independent checkpoints.
- Spatial review: paste a projected polygon and a CSV of points with ID, E, N and role (control, checkpoint or excluded), and declare the CRS.
- Optionally set your own maximum-distance goal from the project specification.
- Read the density figures, duplicates, outside points and the exact largest gap, and export the control register.
How it works
Area per control = A ÷ n; density = 10,000 n ÷ A per ha; area-equivalent spacing = √(A ÷ n) — not an actual spacing. Zero control gives density 0 and an undefined area per control.
Spatial mode measures nearest neighbours, flags duplicate positions and controls outside the polygon, and finds the exact maximum gap: the largest circle centred in the polygon with no control, from Voronoi vertices, Voronoi edges meeting the boundary and polygon corners.
Checkpoints are counted separately and never improve control density. No accuracy is inferred from a count, a density or a gap.
Worked example
50 ha with 8 control points; a 100 m square with corner control. 6.25 ha per control, 0.16 per hectare, area-equivalent spacing √(500,000 ÷ 8) = 250 m. For a 100 × 100 m square with control at the four corners the exact largest gap is at the centre, 70.710678 m from every control.
Frequently asked questions
How many control points do I need?
That comes from your project specification or an applicable mapping standard. Density alone cannot say — the same count can be well spread or bunched.
Can checkpoints count as control?
No. A point used in the adjustment cannot also validate it; keep the roles separate.
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Cite this tool
Zerdly. (2026). Ground Control Density Calculator. Retrieved from https://www.zerdly.com/tools/ground-control-density-calculator/
Tip: Enter any known values to calculate the remaining results.
Designed to run locally in your browser. Tool inputs are not intentionally stored by Zerdly unless stated otherwise.