﻿---
title: Term join
description: Use term joins to augment vector features with properties for data driven styling and richer tooltip content. Term joins are available for the following...
url: https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/4302/explore-analyze/visualize/maps/terms-join
products:
  - Kibana
---

# Term join
Use term joins to augment vector features with properties for [data driven styling](/elastic/docs-content/pull/4302/explore-analyze/visualize/maps/vector-style#maps-vector-style-data-driven) and richer tooltip content.
Term joins are available for the following [vector layers](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/4302/explore-analyze/visualize/maps/vector-layer):
- Configured GeoJSON
- Documents
- EMS Boundaries


## Example term join

The [choropleth layer example](/elastic/docs-content/pull/4302/explore-analyze/visualize/maps/maps-getting-started#maps-add-choropleth-layer) uses a term join to shade world countries by web log traffic. Darker shades symbolize countries with more web log traffic, and lighter shades symbolize countries with less traffic.
![gs add cloropeth layer](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/4302/explore-analyze/images/kibana-gs_add_cloropeth_layer.png)


### How a term join works

A term join uses a shared key to combine vector features, the left source, with the results of an Elasticsearch terms aggregation, the right source.
The cloropeth example uses the shared key, [ISO 3166-1 alpha-2 code](https://wikipedia.org/wiki/ISO_3166-1_alpha-2), to join world countries and web log traffic. ISO 3166-1 alpha-2 code is an international standard that identifies countries by a two-letter country code. For example, **Sweden** has an ISO 3166-1 alpha-2 code of **SE**.
![terms join shared key config](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/4302/explore-analyze/images/kibana-terms_join_shared_key_config.png)


### Left source

The left source for the term join is the [Elastic Maps Service (EMS)](https://www.elastic.co/elastic-maps-service) World Countries. Vector features for this source are provided by EMS. You can also use your own vector features.
In the following example, **iso2** property defines the shared key for the left source.
```
{
  geometry: {
    coordinates: [...],
    type: "Polygon"
  },
  properties: {
    name: "Sweden",
    iso2: "SE"
  },
  type: "Feature"
}
```


### Right source

The right source uses the Kibana sample data set "Sample web logs". In this data set, the **geo.src** field contains the ISO 3166-1 alpha-2 code of the country of origin.
A [terms aggregation](https://docs-v3-preview.elastic.dev/elastic/elasticsearch/tree/main/reference/aggregations/search-aggregations-bucket-terms-aggregation) groups the sample web log documents by **geo.src** and calculates metrics for each term.
The METRICS configuration defines two metric aggregations:
- The count of all documents in the terms bucket.
- The average of the field "bytes" for all documents in the terms bucket.

![terms join metric config](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/4302/explore-analyze/images/kibana-terms_join_metric_config.png)

The right source does not provide individual documents, but instead provides the metrics from a terms aggregation. The metrics are calculated from the following sample web logs documents.
```
{
  bytes: 1837,
  geo: {
    src: "SE"
  },
  timestamp: "Feb 28, 2019 @ 07:23:08.754"
},
{
  bytes: 971,
  geo: {
    src: "SE"
  },
  timestamp: "Feb 27, 2019 @ 08:10:45.205"
},
{
  bytes: 4277,
  geo: {
    src: "SE"
  },
  timestamp: "Feb 21, 2019 @ 05:24:33.945"
},
{
  bytes: 5624,
  geo: {
    src: "SE"
  },
  timestamp: "Feb 21, 2019 @ 04:57:05.921"
}
```

The terms aggregation creates a bucket for each unique **geo.src** value. Metrics are calucated for all documents in a bucket.
The following shows an example terms aggregation response. Note the **key** property, which defines the shared key for the right source.
```
{
  aggregations: {
    join: {
      buckets: [
        {
          doc_count: 4,
          key: "SE",
          avg_of_bytes: {
            value: 3177.25
          }
        },
        ...
      ]
    }
  }
}
```


## Augment the left source with metrics from the right source

The join adds metrics for each terms aggregation bucket to the world country feature with the corresponding ISO 3166-1 alpha-2 code. Features that do not have a corresponding terms aggregation bucket are not visible on the map.
The world country features now have two additional properties:
- Count of web log traffic originating from the world country
- Average bytes of web log traffic originating from the world country

The cloropeth example uses the count of web log traffic to symbolize countries by web log traffic.