Versioning the uMap internal format about umap HOT 2 OPEN

cf #1335
cf #174

from umap.

the umap full backup is a "collection of FeatureCollection", but this case is not handled by the GeoJSON spec AFAIK, so we "invented" a type: "umap", with a layers: [list of FeatureCollection] key; while trying to version our format, let's try to see if there is a more GeoJSON standard way of storing a list of FeatureCollection

@sgillies hey! :) To you have any advice on this specific point ?
Basically, here is how our "umap" export looks like:

{
    "type": "umap",
    "properties": {"some map": "metadata"},
    "geometry": {
        "type": "Point",
        "coordinates": ["the", "map", "default", "center"]
    },
    "layers": [
        {
            "type": "FeatureCollection",
            "_umap_options": {"some layer": "metadata"},
            "features": [{
                "properties": {"some": "props"},
                "geometry": {"some": "geom"}
            }]
        },
        {
            "type": "FeatureCollection",
            "_umap_options": {"some layer": "metadata"},
            "features": [{
                "properties": {"some": "props"},
                "geometry": {"some": "geom"}
            }]
        },
    ]
}

As you see, this mimics a sort of "Collection of collections" type as it could exist in GeoJSON, but it does not AFAIK.

My goal would be to maximise the portability of those data. Eg. someone wants to reimport uMap export in QGis, or the other way around, and retrieve as much as possible of the original structure: data are split into layers, maybe some styling are kept, etc.

Thanks in advance for your input on this :)

from umap.