I am trying to decrease the size of a polygon so to avoid having mixels. Thus, I use the GDAL function buffer:

distance = -5
bufferedGeometry= initialGeometry.Buffer(distance)

In addition, the geometry is in 3857 Projection.

Does -5 mean -5 meters for each point of the polygon's ring?

How does the buffer process takes place?

  • 2
    Please do not ever use EPSG:3857 (Web Mercator) to carry out any sort of distance related analysis. The longitude (X) axis is distorted to infinity as you move north or south of the Equator.
    – Ian Turton
    Jul 14, 2021 at 10:53
  • 1
    @IanTurton thanks for the quick reply. So, what do you recommend for projection regarding apps with distance calculations? 4326? Jul 14, 2021 at 11:48
  • a local project suitable for your data set
    – Ian Turton
    Jul 14, 2021 at 12:12
  • 1
    Basically it is sufficient to know it works, if you want to know exactly you need to dig through GDAL to GEOS to JTS (github.com/locationtech/jts) and read the source code.
    – Ian Turton
    Jul 14, 2021 at 13:05
  • 1
    ESRI has images about how buffers are created desktop.arcgis.com/en/arcmap/latest/tools/analysis-toolbox/… . Negative buffer can only be used with polygons and then the offsets are decreasing the polygon - outer ring is squeezed and holes are made bigger.
    – user30184
    Jul 14, 2021 at 21:30


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