Biodiversity Net Gain Toolkit — Parcel Accounting

Paint mode

Left-click paints the selected habitat as development footprint (destroyed). Right-click (or long-press) paints it as an offset / creation parcel.

Habitat to paint

Offset risk factors

Years to target condition 10 yr

Strategic significance Medium (×1.10)

Biodiversity units

Baseline lost

0.00

Required (+10%)

0.00

Delivered (risk-adj.)

0.00

Net change

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BNG status

Paint some parcels

How it works

This mirrors the real UK Biodiversity Net Gain metric: every habitat parcel is scored in biodiversity units, not hectares alone.

units = area(ha) × distinctiveness × condition × strategic significance

lost      = Σ development parcels  (condition = Moderate, sig = 1.0)
required  = lost × 1.10                      ← statutory net-gain floor
delivered = Σ offset parcels × difficulty
                              × time-discount(years)
                              × spatial risk (on/off-site)

Distinctiveness — grassland (low) through wetland (very high); higher-distinctiveness habitat is worth more per hectare and harder to replace.
Difficulty multiplier — woodland and wetland are slow and unreliable to recreate, so their delivered units are discounted even at full maturity.
Time discount — a unit promised in 30 years is worth less today than one delivered now; the metric penalises long lag between loss and gain.
Off-site — offsetting away from the development site carries a spatial-risk discount versus restoring in place.

Real BNG assessments also weight strategic significance from local nature-recovery strategies and apply per-habitat trading rules (like-for-like or better) — simplified here into one continuous risk stack so the accounting stays legible on one grid.

Grassland (low, ×2) Hedgerow (medium, ×4) Woodland (high, ×6) Wetland (very high, ×8)