How to Make a Slope Map in QGIS in 3 Minutes

Slope is a fundamental calculation of a Digital Elevation Model (DEM) and one of the most important layers for any site assessment. Whether you’re evaluating development suitability, planning drainage and grading, assessing landslide risk, or planning trail routes, a slope map is your first step.

While you can create a basic slope map in QGIS in minutes, understanding how to configure it and how to interpret the results is key for professional use. This guide will walk you through the quick process and explain how to tailor it for your engineering or planning projects.

Slope in QGIS

Step 1

Load DEM Data

High-Resolution DEM: You will need a high-quality Digital Elevation Model (DEM). For accurate slope calculations, especially in developed or complex terrain, we recommend using a high resolution source. You can download LiDAR derived DEMs from public repositories or use Equator’s data menu to access curated, ready to use DEMs for your site.

 

Higgins Bay, New York DEM

2m resolution DEM of Higgins Bay, New York

Step 2

Run Slope tool

Slope is a built in tool in QGIS, you do not need to install any plugins or additional files.

Raster → Analysis → Slope

Configuring the parameters:

  • Input layer – DEM
  • Ratio of vertical units to horizonal – also known as Z factor
    • If your DEM vertical and horizontal units are meters, leave this as 1.
    • If your DEM vertical and horizontal units are feet (common with US data), you must set this to 3.28084 (feet/meter) to correct the calculation.
    • An incorrect Z factor will drastically skew your slope values.
  • Express slope as percent instead of degrees:
    • Degrees are common in geological and natural resource contexts.
    • Percent is standard for engineering and planning (e.g., a 100% slope = 45°).
  • Slope – set a name and location for your new slope raster
QGIS Slope tool example inputs

Slope tool with example inputs

Incorrect Z factor slope raster

Incorrect default Z factor of 1 when using USGS DEM, the default setting cannot be applied when unit is in feet instead of meters. The resulting terrain is flatter than reality due to higher horizontal values.

Correct Z factor slope raster

Correct Z factor of 3.28084 when using USGS DEM, the unit is correctly converted from feet to meters

Step 3

Style and Interpret Your Slope Map

Classifying your raster

The raster result is black and white by default, but the symbology of the raster can be reclassified into different colours and custom groups of values. The symbology can be accessed through double clicking the layer under the Layers pane.

Understanding a slope map

Depending on your symbology, the pixels can be visually categorized into different results. If your symbology represents steep slopes as black, then all of pixels with black are calculated to be steep in elevation differential. Be sure to double check the colour and the corresponding value.

example slope map with schema

Symbology of example slope map

An example of a schema applied to a raster:

0-5%: Gently sloping to flat. Ideal for most construction, agriculture, and drainage.

5-10%: Moderately sloping. Suitable for development with careful planning.

10-15%: Strongly sloping. Significant grading and erosion control needed.

>15%: Steep to very steep. Often has development restrictions, high erosion/landslide risk.

Ready to create professional slope maps for your sites?

Access ready to use, high resolution DEMs for QGIS directly from Equator. Our data requires no prep work, so you can move straight to analysis. Download a DEM for your area of interest and try this tutorial today.

Want to analyze the direction of slopes? Read our companion guide: How to Make an Aspect Map in QGIS