What Is Dissolve?
Dissolve merges adjacent or overlapping polygons into larger combined features. Unlike union which combines all polygons into a single geometry, dissolve can group features by a shared property value — merging only polygons that belong to the same category.
How Dissolve Works
The tool examines all polygon features in your GeoJSON. Adjacent polygons that share a boundary are merged into a single polygon. The internal boundaries between merged polygons are removed, producing a simpler output with fewer features.
This is particularly useful when you have many small polygons (like census tracts or grid cells) that you want to aggregate into larger regions.
Common Use Cases
- Aggregating census tracts into county or state boundaries
- Merging contiguous land use polygons of the same type
- Simplifying parcel data by combining adjacent lots
- Creating generalized regional boundaries from detailed sub-regions
See also: merge (concatenate features), simplifier (reduce vertices).
Try It
Dissolve two adjacent neighborhood rectangles that share a common edge. When dissolved, the internal boundary between them is removed and a single polygon remains:
GeoJSON{
"type": "FeatureCollection",
"features": [
{
"type": "Feature",
"properties": { "borough": "Manhattan" },
"geometry": {
"type": "Polygon",
"coordinates": [[[-73.99, 40.75], [-73.98, 40.75], [-73.98, 40.76], [-73.99, 40.76], [-73.99, 40.75]]]
}
},
{
"type": "Feature",
"properties": { "borough": "Manhattan" },
"geometry": {
"type": "Polygon",
"coordinates": [[[-73.98, 40.75], [-73.97, 40.75], [-73.97, 40.76], [-73.98, 40.76], [-73.98, 40.75]]]
}
}
]
}The output is a single Polygon spanning from -73.99 to -73.97 longitude. The shared edge at -73.98 is removed entirely. Both input features had "borough": "Manhattan", so dissolving by the borough property groups them into one feature.
How It Works
The dissolve tool uses Turf.js (@turf/dissolve), which groups polygon features by the specified property key, then computes the boolean union of all polygons within each group. Polygons that share edges or overlap are merged into a single geometry, while non-adjacent polygons with the same property value become a MultiPolygon. For details on polygon structure, see the GeoJSON specification guide.