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Slope Classification Tool
Overview
The Slope Classification Tool analyses terrain slope distribution within a user-defined area. It classifies the terrain into the Forest Practices Code slope bands and returns the majority slope, a steep country flag, and the area (hectares) and percentage in each band, helping forestry professionals determine whether an area qualifies as "steep country" under regulatory guidelines.
Key Features
- Flexible Area Definition: Draw custom polygons, select existing polygons from a layer, or use preset box and circle shapes
- Layer Selection: Choose from any visible polygon layer (Feature Layer or Map Image Layer with polygon sublayers) as a source for area selection
- Forest Practices Code Bands: Fixed FPC slope bands (≤11°, 11–19°, 19–26°, 26–35°, >35°), matching the Imagery Tool's Slope Logging (FPC bands) colour scheme
- Interactive Shape Editing: Resize and reposition analysis areas with transform tools
- Real-Time Area Display: See the current analysis area in hectares while drawing and editing
- Proportional Results Table: Majority slope and steep country summary, then area (ha), percentages, and a proportional bar for each slope band
- Detailed Report Dialog: Cumulative frequency chart, tabular summary with area calculations, and regulatory definitions
- Steep Country Classification: Automatic determination based on the 20-degree majority slope threshold (per Forest Practices Code 2020)
How to Use the Slope Classification Tool
Accessing the Tool
- Navigate to the Report Tools panel in the right sidebar
- Select Slope Classification from the report tools dropdown
- The tool panel opens showing layer selection, drawing tools, and analysis options
Selecting a Source Layer
The Select from Layer dropdown lists all visible polygon layers on the map. Select a layer to show the Select polygon from layer button, which lets you click on a polygon in that layer to use as your analysis area.
INFO
If no layers appear in the dropdown, ensure at least one polygon layer is visible on the map.
Defining Your Analysis Area
You have four ways to create an analysis area. When a tool is active, a contextual hint appears below the toolbar to guide you (e.g., "Click to add vertices on the map. Double-click or click the first point to finish the polygon.").
Option 1: Select from Layer
- Choose a polygon layer from the dropdown
- Click the Select polygon from layer button (cursor icon), which appears once a layer is chosen
- Click on a polygon in the map belonging to that layer
- The tool attempts to retrieve the polygon using a multi-step fallback: first a direct hit-test, then a spatial query on the Feature Layer, and finally an identify operation for Map Image Layers
- The polygon is highlighted and its area is displayed
Best for: Using existing boundaries such as coupes, cadastre parcels, or management units
Option 2: Draw a Custom Polygon
- Click the Draw Polygon button (polygon icon)
- Click points on the map to define your boundary
- Continue clicking to add vertices as needed
- Double-click to complete the polygon (or press ESC to cancel)
Best for: Irregular areas, custom boundaries, specific study areas
Option 3: Create a Preset Box
- Click the Create a box button (rectangle icon) to create a preset box (default size: 50m x 50m)
- The box appears centred on your current map view
- The shape automatically enters edit mode for immediate adjustment
- Resize using corner handles or reposition by dragging (rotation is disabled; aspect ratio is locked)
- Maximum dimension is 2000m — a warning appears if exceeded
Best for: Rectangular sample areas, standard plot shapes
Option 4: Create a Preset Circle
- Click the Create a circle button (circle icon) to create a preset circle (default radius: 25m)
- The circle appears centred on your current map view
- The shape automatically enters edit mode for immediate adjustment
- Resize using edge handles or reposition by dragging
- Maximum dimension is 2000m — a warning appears if exceeded
Best for: Circular sample plots, radial studies
Editing Your Analysis Area
- Click the Edit Target Shape button (edit icon) to activate edit mode
- For drawn polygons: reshape by moving individual vertices
- For preset shapes: use transform handles to resize and move (rotation is disabled)
- Click elsewhere on the map or toggle the edit button to finish editing
- The area display updates in real time as you edit
WARNING
Preset shapes have a maximum dimension of 2000m. A warning appears if you exceed this limit during editing, and the edit is cancelled.
Slope Bands
Slope is classified into the fixed Forest Practices Code bands below:
| Range | Min | Max | Label |
|---|---|---|---|
| 1 | 0° | 11° | ≤11° |
| 2 | 12° | 19° | 11°<Slope≤19° |
| 3 | 20° | 26° | 19°<Slope≤26° |
| 4 | 27° | 35° | 26°<Slope≤35° |
| 5 | 36° | 99° | 35°<Slope |
A notice in the panel confirms this — "Uses the fixed Forest Practices Code slope bands (set by the analysis service)" — because the bands are applied by the analysis service rather than chosen in the panel. These are the same bands the Imagery Tool's Slope Logging (FPC bands) colour scheme draws, so the report and a symbolised slope raster agree on what each band means. See the Imagery Tool.
Custom degree ranges
Editable min/max/label ranges are not available with the current slope data source. The editor belongs to the alternative Slope VT source, which is temporarily withdrawn (see below); if that source returns, the Custom Degree Ranges switch returns with it.
Slope Data Source
The tool runs against the primary LiDAR-derived slope raster (STT:Slope_tiffs), shown as Slope in the panel.
"Slope VT" temporarily withdrawn
An alternative source, Slope VT (STT:Slope_vt), was previously selectable. It has been temporarily withdrawn by request and is no longer listed, so the picker currently offers one source and nothing needs to be selected before analysing. Nothing else about the tool changes, and the source can be reinstated later.
Running the Analysis
- Ensure your analysis area is defined (area displayed in hectares)
- Click the Analyse button (raster analysis icon)
- Wait while the analysis runs as a job on the slope service. A status row below the buttons shows the job's progress: the job status (e.g., Submitted), then the latest message from the service while it computes, and Completed when it finishes. When the job has posted more than one message, a list button with the message count opens them in a Slope Job dialog
- To stop a running job, click Cancel (shown next to Analyse only while the job runs)
- Results display in a card below the tools
Understanding Your Results
The Slope Classification Results card first shows the Majority slope in degrees (e.g., "Majority slope 18.42°") with a Steep country: Yes or Steep country: No chip (red when Yes), then a table with:
| Column | Description |
|---|---|
| Label | The slope classification range (e.g., "≤11°", "11°<Slope≤19°") |
| Area (ha) | Area in hectares in that slope range |
| % | Percentage of the analysis area in that range |
A proportional bar behind each row provides a visual comparison of the distribution. The footer shows the Total Area: in hectares.
Slope Report Dialog
Click the View detailed slope report with chart and table button (chart icon, shown once results exist) to open the Slope Classification Report dialog. The dialog is resizable and draggable, and contains three tabs: Cumulative Chart, Distribution Table and Definitions.
Cumulative Chart Tab
Displays a Cumulative Frequency of Slopes curve showing the relationship between slope degrees and the cumulative percentage of the analysis area:
- Blue curve: Cumulative frequency line, plotted from the curve the slope service returns
- Red dashed line: 90% threshold — the line at which "majority slope" is evaluated
- Green dashed line: Majority slope value — the degree at which 90% of the area is at or below
- Intersection dot: Where the curve meets the 90% threshold
- Annotation: Displays the calculated majority slope value in degrees (e.g., "Slope at 90%: 18.42°")
Distribution Table Tab
Shows a tabular breakdown of slope ranges with:
- Category (Degrees): Slope classification label
- % of Area: Percentage of the analysis area in the range
- Area (ha): Area in hectares for the range, as returned by the slope service
The table footer includes:
- Total Coupe Area: the total analysed area in hectares
- Majority Slope (degrees): the majority slope value
- Steep Country Coupe: Yes (highlighted in red) if the majority slope is 20 degrees or above, No otherwise
Definitions Tab
Provides regulatory definitions and explanatory notes:
- Notes: "Slope calculations based on Lidar derived 2m by 2m pixels." and how to read the chart's dashed lines
- Majority slope (Forest Practices Code 2020 - Page 95): The maximum steepness of 90% of a coupe area or discrete landscape unit
- Steep country (Forest Practices Code 2020 - Page 98): An area with a majority slope of 20° or more
- Warning: The majority slope calculation is based on the provisional coupe boundary as shown on the map; operational boundaries that vary significantly from the provisional coupe shape may require recalculation
- Note: Directs users to Map Composer for generating printable slope classification reports
Troubleshooting
| Issue | Solution |
|---|---|
| Analyse button is disabled | Draw or select an analysis area first (area must be > 0 ha) |
| No layers in dropdown | Ensure at least one polygon layer is visible on the map |
| "No geometry" error | Draw or select an analysis area before clicking Analyse |
| Analysis fails with error | Try simplifying your polygon or reducing the area size |
| Edit mode won't activate | Ensure an analysis area exists on the map |
| Size limit exceeded warning | Reduce preset shape size to within the maximum dimension |
| Select from layer not responding | Ensure you have selected a layer from the dropdown first |
| Results seem incorrect | Verify analysis area is within DEM data coverage |
| No report button | Run the analysis first; the button appears with the results |
Frequently Asked Questions
Q: What is "majority slope"? A: Majority slope is the slope value at which 90% of the analysis area is at or below that gradient. It is the 90th percentile of the slope distribution within the analysis area.
Q: What defines "steep country"? A: An area is classified as steep country when the majority slope is 20 degrees or greater. This threshold is based on forestry regulatory guidelines.
Q: Can I use Map Image Layer polygons for area selection? A: Yes. The tool supports both Feature Layers and Map Image Layers with polygon sublayers. For Map Image Layers, the tool uses an identify operation to retrieve the polygon geometry when you click on the map.
Q: How accurate is the slope analysis? A: The analysis uses a pre-computed LiDAR slope raster (2m by 2m pixels) derived from DTM data, processed by an ArcGIS Server geoprocessing job. Accuracy depends on the resolution and quality of the underlying DTM. The geometry is reprojected to EPSG:28355 for analysis.
Q: Can I change the slope ranges? A: Not at present. The tool reports the fixed Forest Practices Code bands, which the analysis service applies. The editable ranges belonged to the Slope VT data source, which is temporarily withdrawn.
Q: How do I get a printable report? A: Use Map Composer for generating printable slope classification reports. The Slope Report Dialog in Horizon provides an interactive preview of the chart and table data.