# Draw buffer around points considering slope in QGIS

I generated random points on a map. Around each point I would like to draw a circular buffer which considers the slope in that area, and within these circular buffers I would monitor tree height in the field.

It is very important for the polygons to consider the slope because I would always like to have the same surface area in each polygon. So I assume that when drawing a circular buffer it will turn out ellipsoidal on a area with a slope.

• I suppose you could create ellipsoids around your points, using the direction of the slope for orientation, and its steepness as a factor for calculating the minor extent of the ellipsoid. Applied trigonometrics.
– Erik
Feb 7 at 10:48
• in most cases the vertical variation will be negligible for the area, unless you are looking at very steep slopes over very short distances Feb 7 at 11:00
• The monitoring plots will have a radius of just 8-15meters and the terrains that we are working in have steep slopes. So unfortunately we found out that we cannot neglect the slopes. Feb 7 at 11:22
• @Erik is there a way to do this automatically. It seems like such an easy and basic necessity. I really only want to draw a polygon of a specified radius considering the slope. Feb 7 at 11:26
• I told you how to do it automatically? What else do you need?
– Erik
Feb 7 at 11:34

4. Field calculate the ellipse major axis: `cos(radians("slope1"))*50`
5. Geometry by expression: `make_ellipse(\$geometry, "major", 50, "aspect1")`