Explode multi-geometries

What this tool does

It walks each feature and, when the geometry is a multi-part type, emits one feature per part: MultiPoint → Points, MultiLineString → LineStrings, MultiPolygon → Polygons, and a GeometryCollection → one feature per member geometry, flattened recursively. Single-part features pass through untouched.

The intent it closes: "I need to work on these parts individually." That covers styling or labelling each island separately, computing per-part area, joining attributes at part level, or feeding a tool that only accepts single-part geometries — which includes a surprising amount of GIS software and most simple renderers.

How this tool works

One pass, with the split rule depending on the geometry type.

1. Identify the parts

For a multi-geometry, each element of the top-level coordinates array is one part; for a GeometryCollection, each member geometry is one part, with nested collections flattened. A single-part geometry has exactly one part, so it comes through unchanged. Features with a null geometry are preserved as-is rather than dropped.

2. Copy the properties

Every produced feature gets a copy of the original properties — so five islands each carry the country name they came from. With add _part / _parent on, and only where a feature actually split, two extra properties are added: _part numbering the part within its feature and _parent numbering the source feature. Those two are all you need to reassemble or to group later.

3. Emit the collection

The result is a flat FeatureCollection in the original order — feature 1's parts, then feature 2's. The status line reports the before and after counts, which is the quickest way to see how multi-part your data actually was.

Options

Split into

Single-part geometries is the normal choice: the geometry type changes from Multi… to its singular form and the shape is unchanged. One point per vertex is a different job — it discards the shape and emits a Point feature for every position in the file, which is how you inspect vertex density, feed a point-clustering tool, or export a coordinate list.

add _part / _parent

Numbering is only added to features that actually split, so a file of single-part geometries comes out with no extra properties at all. Use _parent to group the parts back together — in a spreadsheet after a CSV export, or with the filter to isolate one original feature.

Example

Input:

{ "type": "Feature",
  "properties": { "country": "NZ" },
  "geometry": { "type": "MultiPoint", "coordinates": [[174.7,-36.8],[172.6,-43.5]] } }

Output:

{
  "type": "FeatureCollection",
  "features": [
    { "type": "Feature", "properties": { "country": "NZ", "_part": 1, "_parent": 1 },
      "geometry": { "type": "Point", "coordinates": [174.7, -36.8] } },
    { "type": "Feature", "properties": { "country": "NZ", "_part": 2, "_parent": 1 },
      "geometry": { "type": "Point", "coordinates": [172.6, -43.5] } }
  ]
}

One feature became two, each keeping country. Because the split happened, both gained _part and _parent; a feature that did not split would have neither.

Tips & common pitfalls

• Polygon holes stay with their polygon. Exploding a MultiPolygon splits it into polygons, each with its own exterior ring and holes intact. Rings are never separated from their parent.
• Attribute duplication is the trade. Every part carries a full copy of the properties, so a heavily multi-part file grows. That is the price of working per part; stats shows the before/after size effect.
• Vertex mode can be enormous. A detailed coastline has tens of thousands of positions, and each becomes a feature. Simplify first if you are exploring rather than exporting.
• There is no implode. Reassembling parts into multi-geometries means grouping by _parent, which is a job for a script or a GIS dissolve — this site does not have that tool.

FAQ

Why do I need single-part geometries?

Many tools and formats only handle them: some renderers style per feature, per-part measurement needs separate features, and several import paths reject multi-geometries outright. It is also the easiest way to label each island or each segment individually.

Does it flatten GeometryCollections?

Yes, recursively — every leaf geometry inside becomes its own feature, so nested collections do not survive.

What happens to features that are already single-part?

They pass through unchanged, and with numbering on they gain no extra properties, since nothing split.

Is anything uploaded?

No. The whole operation runs in your browser.