Slope layer with false results in QGIS? [duplicate]

Question

After the DEM creation, I wanted to create slope layer.

However, the result has not satisfied me. I don't think the slope map is correct. Have you ever encountered false calculated terrain map?

This is the DEM:

And this is the slope layer.

Answer 1

As mentioned in comments by user30184 and GerardoJimenez this is due to the horizontal coordinates x and y having a different unit of measurement from the elevation coordinate z.

For example, having latitude and longitude in degrees and elevation in meters.

So either:

• Reproject the CRS to a projected coordinate system (e.g. Changing projection of geotiff file (raster data) in QGIS?), or
• Scale the ratio between vertical and horizontal units (e.g. Scale and Z factor have no effect on hillshade analysis in QGIS).