What you will make

A terrain-screening map with the specified slope bands, source and resolution note, and a clear explanation of what the screening can and cannot establish.

Slope can help a planner identify terrain that deserves closer review. A raster slope value is calculated from elevation data and its scale, units, resolution, and method matter. Screening classes do not determine buildability, erosion, landslide likelihood, or regulatory status.

• Distinguish a DEM, a slope raster, and contour lines.
• Identify percent-rise slope values and apply the stated screening bands.
• Describe uncertainty and avoid treating the map as a hazard or development determination.

Work through the method

1. Check the elevation source

   Record the DEM source, date, cell size, vertical units, and horizontal coordinate system if supplied. Verify that the study boundary overlaps the surface and note NoData edges. If these details are absent, label them unavailable.

   Check your work: Your map notes which terrain-source details are known and unknown.

2. Prepare a slope surface

   With a licensed Slope tool, choose Percent rise and one documented method. For Planar, use a projected horizontal CRS and set z-factor to convert vertical units into horizontal units: elevation in feet and horizontal metres needs 0.3048; matching units uses 1. For Geodesic, specify the actual elevation Z unit instead. Do not assume these controls match Surface Parameters. Without an available license or a documented supplied percent-slope raster, pause the calculation and request the input rather than inventing a result.

   Check your work: The layer is explicitly identified as percent slope, not degrees.

3. Apply the requested bands

   Use symbology or reclassification to show under 15%, 15 to under 20%, 20 to under 25%, and 25% or greater. State how exact break values are assigned so adjacent classes do not overlap.

   Check your work: A value of 15 belongs only to the 15–under-20 class; 20 to 20–under-25; 25 to 25-plus.

4. Add terrain context

   If supplied contours are available, add them as context and label the contour interval only when the source documents it. Creating new contours from a DEM requires a surface tool and an appropriate license; do not imply the contours are authoritative survey lines.

   Check your work: Contour provenance and interval are either documented or clearly marked unavailable.

5. Read the pattern

   Describe where steeper classes appear relative to the study boundary and other layers. Use phrases such as terrain-screening class and warrants closer review. Do not label a slope band as a hazard, unsafe area, or prohibition without applicable evidence and professional review.

   Check your work: Your summary separates mapped terrain from any planning or engineering judgment.

6. Export with limitations

   Add a source note with DEM date, resolution, units, method, and license path if known. Export PDF or PNG. Include a short note that slope screening is not a site-specific geotechnical or regulatory determination.

   Check your work: The map communicates both the bands and the limits of the screen.

Make a terrain-screening map

1. Inspect supplied DEM metadata or document which details are unavailable.
2. Use the provided percent-slope raster, or create one only if the required extension is licensed.
3. Map under 15%, 15–under 20%, 20–under 25%, and 25% or greater.
4. Add documented contours if supplied and write a non-hazard screening caption.

Bring the method into a product

• Terrain-screening map
• Methods and limitations note

Suggested formats: PDF, PNG.

Reflect: What site-specific evidence would be needed before a planning team treats this screen as a constraint?

Avoid these mistakes

• Percent rise is not degrees; at 45 degrees a surface is 100 percent rise.
• DEM resolution, units, and processing choices affect the mapped values.
• Slope bands and contours do not establish hazard, safety, permit status, or engineering suitability.