Support GeoJSON MultiPolygon

[simon04]

@tyrasd in #206 (comment):

Well, actually, there are already a couple of "multipolygon" sources in the repo (for example the South Tyrol 2014, or the Tiris * imagery), but which we forgot about in the geojsonification process in #191. Instead, they continued to use the slightly odd (and incompatible to GeoJSON) convention where the rings in the coordinates array are all outer rings and inner rings are not allowed.

It's probably best to fix those all in one go and to apply an additional fix (very similar to yours also to fix the legacy json output).

For this particular layer this means that we can either wait until this is all fixed in the data processing before adding the source, or that we merge it using the old&incorrect coordinate scheme (because the PR as-is will probably break things for users of our legacy-json output).

[simon04]

Change in convert_xml.py to support MultiPolygon:

diff --git a/scripts/convert_xml.py b/scripts/convert_xml.py
index f2a0b34..47ea57a 100644
--- a/scripts/convert_xml.py
+++ b/scripts/convert_xml.py
@@ -68,7 +68,7 @@ for source in sources:
     if geometry:
         bounds = ET.SubElement(entry, "bounds")

-        for ring in geometry['coordinates']:
+        for ring in geometry['coordinates'] if geometry['type'] != 'MultiPolygon' else [ring for rings in geometry['coordinates'] for ring in rings]:
             shape = ET.SubElement(bounds, "shape")
             for p in ring:
                 point = ET.SubElement(shape, "point")

[rbuffat]

@andrewharvey @bhousel
MultiPolygons would be handy for many sources. Is there a reason that MultiPolygons are not allowed? Are there editors that would break? It looks as some sources use interior rings of Polygons to "emulate" MultiPolygons, which leads to invalid geometries.

[bhousel]

MultiPolygons would be handy for many sources. Is there a reason that MultiPolygons are not allowed? Are there editors that would break? It looks as some sources use interior rings of Polygons to "emulate" MultiPolygons, which leads to invalid geometries.

No reason.. I'd actually prefer for the geometries be proper GeoJSON multipolygons.
And I've already gone thru and fixed them all.. twice 🙄

[rbuffat]

No reason.. I'd actually prefer for the geometries be proper GeoJSON multipolygons.
And I've already gone thru and fixed them all.. twice

Then I assume you are happy about #857

[rbuffat]

Implemented with #1450