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How can you combine GeoJson features by their property value?

TLDR: Can you join together GeoJSON features that have a common property, such that the final polygon is a combination of the smaller features?

I’m building a web application that requires me to modify some existing GeoJSON by removing lines between counties, essentially creating larger polygons out of smaller ones. Here’s what the GeoJSON looks like:

JavaScript

In this dummy example, I’d like to join together Alameda County and Fremont West, because they both contain the “joiner” property of 1 (they are next to each other, this is a given). Visually speaking, this would mean that certain adjacent polygons on the map would be joined into a single polygon.

This is what the data currently looks like when projected using MapboxGL:

Original GeoJSON

The final projection would join together adjacent polygons with a common property and remove the dividing lines, creating larger ones:

Joined GeoJSON

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Answer

You can use Turf’s “dissolve” method, which does exactly this:

JavaScript

Documentation: http://turfjs.org/docs/#dissolve

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