03 - Filtering nodes that have a tag

//find all the nodes in this box around Uluṟu [bbox:-25.38653, 130.99883, -25.31478, 131.08938]; //but limit to just those nodes that have a name tag node["name"]; //TRYME #1 the above two statements are equivalent to the following. //use this form if you need to query for features in several //different bounding boxes //node(-25.38653, 130.99883, -25.31478, 131.08938)["name"]; //TRYME #2 try finding just nodes that have a Pitjantjatjara name //node["name:pjt"]; //use out body to include tags in the output, so //we can inspect the results out body;

This query demonstrates how to filter nodes based on their tags.

This is a useful and important feature. You'll be using it a lot in your queries.

Tags in OpenStreetMap are used to attach information to nodes, ways and relations. There is an ever growing list of tags used to capture different types of data.

Often, when we're querying the database we're not interested in all of the nodes (or ways or relations) in an area. Just those tagged as a specific type.

We can specify filters in our Overpass QL queries to restrict the results to just those features that have specific tags and values.

Tag filters as defined within square brackets ([]). This query adds a filter to the node statement:

node["name"]

This limits the set of returned nodes to those that have a name tag, regardless of its value.

As we saw in the previous example, many nodes in the OpenStreetMap data are there to help define larger geospatial features. They aren't all individually points of interest. So they don't typically have any tags attached to them.

When you run this query you'll see that there are now only around 30 nodes returned compared to the 4,000 or so returned in the previous examples.

OpenStreetMap is a multilingual map. And some tags, like names, might have values in several different languages.

The OSM data model doesn't allow tags to have multiple values, e.g. one per language. Instead we use multiple tags, which are qualified by a language code.

For example, if we wanted to find nodes that have a name in Pitjantjatjara, which is the dialect spoken by the people that live around Uluṟu, then we would instead filter for a tag called name:pjt.

Who gets to decide what goes in the default name tag? That's something for local mappers to discuss and agree on. See the links below for more information.

Links	https://wiki.openstreetmap.org/wiki/Key:name https://wiki.openstreetmap.org/wiki/Multilingual_names https://en.wikipedia.org/wiki/Pitjantjatjara https://en.wikipedia.org/wiki/Pitjantjatjara_dialect
Source File	03-nodes-basic-filter.osm
Authors	Leigh Dodds