VRA and Zones

The portal can compute zones four different ways. Each method handles NDVI distributions differently. This page tells you when to reach for which.

Quick reference#

Method	What it does	When to use
K-Means	Clusters NDVI values by similarity into N groups.	Default. Works on most fields with reasonably continuous NDVI.
Jenks Natural Breaks	Minimizes variance within each class while maximizing variance between classes.	Bimodal or multi-modal NDVI distributions. Stressed pockets separated from healthy main field.
Quantile	Splits the data into N equal-sized groups by area.	When you want each zone to cover roughly the same number of acres.
Equal Interval	Divides the NDVI range into N equal intervals.	When you care about absolute NDVI ranges (e.g., "0.4 to 0.5" matters), not relative groupings.

Picking the zone count#

The wizard exposes three presets — Low / Medium / High. Internally these map to a number of clusters:

Preset	Clusters
Low	2
Medium	3
High	5

Rule of thumb: more zones is not always better. Each additional zone adds complexity to the application and increases the chance of motor / valve transitions during the flight (which adds error). For most fields, 3 zones (Medium) is the sweet spot.

Block size#

Block size is the resolution at which NDVI is sampled and the prescription is rendered:

• 3–5 m — very fine. Picks up small patches. Larger output file. Use for high-value crops or precision research.
• 5–10 m — balanced. Default for soybean, corn, cotton at typical farm scales.
• 10–20 m — coarse. Use for very large fields where the drone's swath is wide and fine differences won't be flown anyway.
• 20–50 m — broad strokes. Useful for uniform fields where you just want a 2-zone "high vs. low" split.

Choosing a preset#

The three application presets decide how rates are distributed once zones are computed:

Recovery#

Applies more product where NDVI is low. The logic: areas of stress need help, so concentrate inputs there. Best for:

• Foliar fertilizer rescue passes.
• Targeted micronutrient corrections.
• Stressed corners that have responded to similar interventions in past seasons.

Maintenance#

Applies more product where NDVI is high. The logic: protect the high-yield zones; the stressed areas are likely not going to respond and the spend isn't worth it. Best for:

• Late-season fungicides protecting the canopy.
• Boron / micronutrient maintenance.
• Variety trials where you want to maintain the best-performing strip.

Neutral#

Uniform rates across all zones. Useful as a baseline export — the shapefile still respects the plot boundary and exclusion zones, but every zone gets the same rate.

Thresholds#

The wizard exposes two thresholds:

• Lower Threshold — NDVI < value is treated as Bare Soil / Low Vigor (Zone 1).
• Upper Threshold — NDVI ≥ value is treated as High Vigor (last zone).

Use them to override the clustering at the edges. For example, you can force any NDVI below 0.15 to be ignored (treated as bare soil) regardless of what the clustering says.

Bulk editing#

After zones are generated:

• Box-select multiple blocks on the map (the count appears in the panel).
• Set a single rate in the Bulk Editing panel.
• Click Apply.

This is the fastest way to "smooth" odd zones — for example, eliminating a one-block patch of Zone 5 inside an otherwise-Zone 3 region.

Redistributing blocks#

The Redistribute Blocks tool lets you reassign blocks zone-by-zone. Useful when:

• The clustering put two adjacent blocks in different zones for no agronomic reason (e.g., shadow from a windbreak).
• You want to manually correct a known field-edge artifact.

Pick the target zone, then click any block on the map to assign it.

Merging zones#

Two zones too similar to bother distinguishing? The Merge Zones action collapses adjacent selected zones into one. The merged zone takes the higher zone number's rate. The Statistics panel updates immediately.

Exclusion zones#

Always draw exclusion zones last, after you've finalized rate by zone. The exclusion polygon overrides everything else: the controller will simply not apply any product inside the exclusion. Common uses:

• Waterways and drainage ditches.
• Field edges where you don't want overspray on a neighboring property.
• Sensitive corners (apiaries, pollinator strips).

You can draw multiple exclusion zones; they don't have to be connected.

Sanity checks before downloading#

Before clicking Generate VRA Prescription, verify:

1. Statistics → Avg NDVI matches what you remember from the field. Wildly off? Something's wrong with the source imagery.
2. Zone count matches what you intended.
3. Min / Max rates in the Application Rate by Zone panel are within your sprayer/seeder's mechanical range.
4. No tiny "speckle" zones (single blocks of an outlier zone) — merge or redistribute them.
5. Exclusion zones are drawn where you need them.

After downloading, see Exporting shapefiles for what's in the zip.

Related#

• Management Zones concept — the math behind each method.
• VRA Prescription concept — what variable-rate application is and isn't.
• NDVI concept — interpreting the underlying signal.