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Plot Random Tool ​

Overview ​

The Plot Random Tool generates spatially distributed random sample plot locations within selected polygon boundaries. This tool is designed for field sampling, forest inventory, and ecological survey planning, providing grid-based plot distribution with numbered point markers displayed directly on the map.

Key Features ​

  • Layer Selection: Choose from any visible polygon layer (Feature Layer or Map Image Layer with polygon sublayers)
  • Interactive Polygon Selection: Click polygons on the map to select analysis boundaries with toggle behaviour
  • Multiple Polygon Support: Select multiple polygons and generate plots across all selected areas
  • Configurable Plot Density: Set the number of hectares per plot to control sampling intensity
  • Grid-Based Distribution: Plots are spatially distributed within selected polygons with minor random offset for natural placement
  • Numbered Plot Labels: Each generated plot displays a sequential number for easy field identification
  • Map Image Layer Support: Select polygons from server-based layers with result cycling through overlapping features
  • Geodetic Area Calculation: Accurate area measurements accounting for Earth's curvature

How to Use the Plot Random Tool ​

Accessing the Tool ​

  1. Click the Random Plot Generator button (layer-points icon) in the toolbar
  2. The tool panel opens showing layer selection and configuration options

Step 1: Select a Target Layer ​

Choose a visible polygon layer from the Target Layer dropdown. The list includes all Feature Layers with polygon geometry and Map Image Layers with polygon sublayers that are currently visible on the map.

INFO

If the dropdown is empty, make sure at least one polygon layer is turned on in the layer panel.

Step 2: Select Polygons ​

  1. Click the Select Target Shape button (cursor icon) to activate selection mode
  2. Click on polygons in the map to select them — selected polygons are highlighted
  3. Click a selected polygon again to deselect it
  4. The Total (ha) display updates as you add or remove polygons

For Map Image Layer data, clicking the same location multiple times will cycle through overlapping polygon results. A notification shows which result you are viewing (e.g., "feature 1 of 3", "feature 2 of 3"). The cycle wraps around to the first result after the last one.

Step 3: Configure Plot Density ​

  • Enter a value in the One Plot In [Ha] field to specify how many hectares each plot represents
  • For example, entering 2 means one plot will be generated for every 2 hectares of selected area
  • The default value is 2 ha per plot
  • The field range is 1 (minimum) to Max Plot Density (maximum)

The Max Plot Density value equals the total selected area rounded down to the nearest whole hectare. It sets the upper limit of the One Plot In field, ensuring that even at the coarsest setting you still get at least 1 plot. The value updates automatically as you select or deselect polygons, and the One Plot In value is capped to it if the area shrinks.

Step 4: Generate Plots ​

  1. Click the Generate Random Plots button
  2. Any previously generated plots are cleared before new ones are created
  3. Random plot points are created within the selected polygon boundaries
  4. Each plot is displayed on the map as a numbered point marker (1, 2, 3, etc.)

Resetting ​

Click the Reset button to:

  • Clear all selected polygons from the map
  • Remove all generated plot markers
  • Deactivate selection mode
  • Return to a fresh state for new plot generation

Troubleshooting ​

IssueSolution
No layers in dropdownEnsure at least one polygon layer is visible on the map
Cannot select polygonsActivate selection mode by clicking the Select button first
Plots generated outside boundaryThis is unlikely; try regenerating or selecting a new polygon
Very few plots generatedReduce the hectares-per-plot value to increase density
Select button not respondingChoose a target layer from the dropdown first
Map Image Layer polygons not selectableVerify the layer has polygon sublayers visible

Frequently Asked Questions ​

Q: Can I select polygons from multiple layers? A: No, plots are generated from polygons selected from a single target layer at a time. However, you can select multiple polygons within that layer.

Q: How are plot locations determined? A: Plots are distributed using a grid-based algorithm with a minor random offset applied to each point. This ensures even spatial coverage while avoiding an overly rigid pattern.

Q: Can I export the generated plot locations? A: Currently, plots are displayed on the map during the session. Use the Print tool to capture the map with plot locations, or note the coordinates from the map display for field use.

Q: What happens if my selected area is very small? A: The tool will generate fewer plots or a single plot if the area is smaller than the specified density. Adjust the hectares-per-plot value to suit smaller areas.

See Also ​

Horizon Help Documentation

Sustainable Timber Tasmania