Donut Polygons were the nightmare in first GIS courses. At the very moment I can’t remember why but the concept of an inner and an outer part makes total sense in the real world (house with a patio, lakes with islands, Rome with the Vatican City) yet the creation of those was never the covered in the basic “how to edit”-classes. So how can we create them with QGIS, ArcMap as well as ArcGIS Pro and geoJSON? In this tutorial I will cover this basic task.
Mapshaper by mbloch is one of my favourite “swiss army knife”-tools if you need fast data reduction and topology first aid in polygon data handling. There a two versions of mapshaper. The first is a hosted webservice: www.mapshaper.org, where you can easily upload .shp-, GeoJson- or TopoJson-Files via drag&drop or folder selection. Afterwards you have to chose your simplification method (Douglas-Peucker, Visvalingam or modified Visvalingam) and some other options like “repair intersections”, “auto snap” and “prevent shape removal” and you’re ready to go.