add new topological information

[ericemc3]

It is a feature request, considering the unique topological decomposition process which is at the center of mapshaper. Such as the this.partCount property, would it be possible to add (after running a specific processing command), for polygons layers, these properties for each feature:

• hasHoles : 1 or 0 (or true/false),
• something like the inner/outer property for lines, allowing to filter polygons on the edge of a layer (with at least one boundary which is not shared with another polygon and which is not part of a hole),
• a categorical value in the range 1-4, derived from the four colors theorem, allowing to color polygons nicely (2 adjacent polygons do not share the same value),
• a list of comma-separated fids (feature ids) describing all neighbours for one polygon.

[mbloch]

These are all good suggestions, thanks :)

[ericemc3]

BTW, i have written my first Mapshaper tutorial: https://www.icem7.fr/outils/mapshaper-visualiser-et-affiner-des-fonds-de-carte-en-ligne/