Extracting Nodes and Ways from Multipolygon Relationships in OpenStreetMap Using Overpass API

Learn how to efficiently extract all nodes and ways from multipolygon relationships in OpenStreetMap that have at least one tag using the `Overpass API`.
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Extracting Nodes and Ways from Multipolygon Relationships in OpenStreetMap Using Overpass API

OpenStreetMap (OSM) is a fantastic resource for geographic information, but sometimes extracting specific data can be challenging. If you're looking to extract all nodes and ways from multipolygon relationships that contain at least one tag using the Overpass API, you're in the right place. In this post, we will explain how to structure your Overpass queries to achieve this goal effectively.

Understanding the Problem

When working with OSM data, relationships, especially multipolygon types, are often complex. Since these multipolygon relationships can encompass various geographic features, it becomes essential to filter out nodes and ways that have meaningful tags. In this guide, we will break down the steps needed to extract only the relevant data using the Overpass API.

Step-by-Step Solution

Basic Query Setup

First, we need to define the geographic bounding box that contains the multipolygon relationships we want to query. Here's how you can set up your query:

[[See Video to Reveal this Text or Code Snippet]]

This line defines the area for which the query will be executed.

Extracting Multipolygon Relationships

Next, we will filter for multipolygon relationships using the following code:

[[See Video to Reveal this Text or Code Snippet]]

This part of the query captures all relationships of type multipolygon and assigns them to a variable called .relation.

Extracting Ways with Tags

Now, to extract all ways associated with these multipolygon relationships that contain at least one tag, use this segment of the query:

[[See Video to Reveal this Text or Code Snippet]]

Here’s what’s happening:

if:count_tags() > 0 filters these ways to only those that contain one or more tags.

Complete Query Example

Combining all of the above, the complete Overpass API query would look like this:

[[See Video to Reveal this Text or Code Snippet]]

This query will extract all the relevant ways from the multipolygon within the specified bounding box.

Filtering Ways Further (Optional)

If you want to refine your results further by filtering out specific types of ways (like highways or tunnels), you can use the following code:

[[See Video to Reveal this Text or Code Snippet]]

Wrapping Up

By following the steps outlined in this blog, you can successfully extract all the nodes and ways from multipolygon relationships using the Overpass API. This method ensures that you only pull in data that is relevant and carries tags, making your OSM queries precise and useful.

We hope this guide helps you streamline your OpenStreetMap data extraction process, saving you time and effort in the future!