What are tags in OpenStreetMap?

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On OpenStreetMap (OSM), volunteers around the world work together to continuously create a map that contains everything the creators find relevant. The special thing about it: Anyone can join in and add, change or correct information. One concept is particularly important in order to capture all the details, from streets and buildings to bicycle racks and drinking water fountains: the so-called “tags”. But what exactly are these tags and why are there so many of them?

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What are tags?

Simply put, tags are small descriptions or “labels” for the objects on the map. For example, if you mark a street on OSM, you can use tags to specify whether it’s a main road, a pedestrian zone or a cycle path. Or let's say you have added a park - then you can describe it with tags such as “name=city park”, “amenity=bench” for benches or “natural=tree” for trees. A tag always consists of a “key” and a “value”, for example “highway=residential” for a residential street.

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Who defines the tags?

You might assume that OSM has an official structure that defines all tags - but this is not the case. Instead, the system is open: The OSM community itself decides which tags are useful and which are less so. There are, of course, some “standard tags” that have become established worldwide, such as “highway” for roads or “building=yes” for buildings. There is also documentation for all these standard tags on the OSM wiki page.

However, new tags are constantly being created because the community has new needs or other things are relevant in other countries. It’s therefore possible that there are slightly different tags for the same object in different countries or that someone introduces a new tag that no one has used before. This makes the system flexible, but also a little chaotic at times.

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Why are there so many different tags?

The main reason for the large number of tags in OpenStreetMap (OSM) is the wide variety of objects recorded and the ability to describe them in great detail. You can enter far more than just streets and buildings in OSM - from cycle paths and park benches to light poles and art sculptures. This flexibility makes it possible to reflect local characteristics and individual interests, which is why users from different regions introduce new tags.

One example is cycle paths. Here there are various tags to define details, such as

• Basic type: “highway=cycleway” for cycle paths or “cycleway=lane” for marked cycle lanes on the road
• Condition: “surface=asphalt” for asphalt or “surface=gravel” for gravel
• Access rights: “bicycle=designated” for cycle paths that are only open to bicycles, or “foot=yes” if pedestrians are also allowed to use them

This variety makes OSM very flexible, but can also lead to confusion as there are no fixed specifications - so the same objects may be tagged differently in different countries or regions.

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Advantages & disadvantages of the tag system in OSM

The tag system in OpenStreetMap offers many advantages. It’s extremely flexible and makes it possible to map almost anything that’s relevant to the community - from frequent hydrants to special hiking trails for rare plant species. Since any user can suggest and use new tags, the map remains dynamic and constantly adapts to new requirements. The adaptability to local conditions is also helpful: The lack of a central instance for specifications means that regional characteristics and cultural differences can be mapped in detail, making the map versatile and globally relevant.

At the same time, the tag system also has its disadvantages. The large number of tags and variants can quickly become confusing, which is particularly challenging for new users, as they first have to familiarize themselves with the common regional tags and their meaning. In addition, the free use of tags can lead to inconsistencies, which can later cause problems during data analysis or uniform presentation. Finally, the tagging system harbors potential for conflict: as ideas about how something should be mapped often differ, there are always discussions within the community - which makes co-creation lively, but sometimes also difficult.

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Summary

Tags are the heart of OpenStreetMap and what makes the map so flexible and individual. Even if the multitude of tags can sometimes seem confusing, it’s precisely this openness that makes OSM so detailed and diverse. The community is constantly developing the system further, and this is exactly what makes OpenStreetMap unique: it’s a map by and for people around the world who want to map their surroundings in as much detail as possible.

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