GIS catchment overlap accounting calculator

Calculate population covered at least once and population in overlapping service areas with your own figures.

Your numbers

Use the units shown. Results update as you change valid inputs.

Use population covered at least once and population in overlapping service areas to compare changes to your inputs. The method and limits below explain the scope.

Examples

Examples

Try the starting example

Population cell centers [x,y,population]
[[1,1,100],[3,1,200],[8,1,50]]
Service polygon exterior rings
[[[0,0],[4,0],[4,4],[0,4]],[[2,0],[6,0],[6,4],[2,4]]]
Population covered at least once
300
Population in overlapping service areas
200
Per-zone gross covered population
[300,200]

Try another scenario

Population cell centers [x,y,population]
[[1,1,150],[3,1,200],[8,1,50]]
Service polygon exterior rings
[[[0,0],[4,0],[4,4],[0,4]],[[2,0],[6,0],[6,4],[2,4]]]
Population covered at least once
350
Population in overlapping service areas
200
Per-zone gross covered population
[350,200]
Calculation method

Calculation method

Population covered at least once

Sum cell-center populations with any polygon match; no double count.

Population in overlapping service areas

Sum cells matching more than one zone.

Per-zone gross covered population

Zone totals overlap deliberately; do not add them for total reach.

Symbols and units
a
Population cell centers [x,y,population]
b
Service polygon exterior rings

Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.

Assumptions & limits

Assumptions & limits

  • Service polygons, population cells, overlap policy. Returns Population coverage without double counting. All coefficients and observations are user supplied; results describe only the stated mathematical model. Quantities are deterministic calculations from supplied observations and assumptions; no external data is fetched. Supported limits: Finite inputs only; numeric fields bounded as labelled. Lists and JSON records are limited to 256 entries unless a stricter tool bound is stated. No automatic design approval, legal conclusion, treatment recommendation or safety certification.
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