<!-- NOTE! Check on https://github.com/gohugoio/hugo/issues/2826 for shifting of terms' pages to .Data.Pages AND
https://discourse.gohugo.io/t/how-to-specify-category-slug/4856/15 for original discussion.-->
Hugo includes support for user-defined groupings of content called **taxonomies**. Taxonomies are classifications that demonstrate logical relationships between content. See [Taxonomies under Content Management](/content-management/taxonomies) if you are unfamiliar with how Hugo leverages this powerful feature.
Hugo provides multiple ways to use taxonomies throughout your project templates:
* Order the way content associated with a taxonomy term is displayed in a [taxonomy list template](#taxonomy-list-template)
* Order the way the terms for a taxonomy are displayed in a [taxonomy terms template](#taxonomy-terms-template)
* List a single content's taxonomy terms within a [single page template][]
## Taxonomy List Templates
Taxonomy list page templates are lists and therefore have all the variables and methods available to [list pages][lists].
### Taxonomy List Template Lookup Order
See [Template Lookup](/templates/lookup-order/).
## Taxonomy Terms Template
### Taxonomy Terms Templates Lookup Order
See [Template Lookup](/templates/lookup-order/).
### Taxonomy Methods
A Taxonomy is a `map[string]WeightedPages`.
.Get(term)
: Returns the WeightedPages for a term.
.Count(term)
: The number of pieces of content assigned to this term.
.Alphabetical
: Returns an OrderedTaxonomy (slice) ordered by Term.
.ByCount
: Returns an OrderedTaxonomy (slice) ordered by number of entries.
.Reverse
: Returns an OrderedTaxonomy (slice) in reverse order. Must be used with an OrderedTaxonomy.
### OrderedTaxonomy
Since Maps are unordered, an OrderedTaxonomy is a special structure that has a defined order.
```go
[]struct {
Name string
WeightedPages WeightedPages
}
```
Each element of the slice has:
.Term
: The Term used.
.WeightedPages
: A slice of Weighted Pages.
.Count
: The number of pieces of content assigned to this term.
.Pages
: All Pages assigned to this term. All [list methods][renderlists] are available to this.
## WeightedPages
WeightedPages is simply a slice of WeightedPage.
```go
type WeightedPages []WeightedPage
```
.Count(term)
: The number of pieces of content assigned to this term.
.Pages
: Returns a slice of pages, which then can be ordered using any of the [list methods][renderlists].
## Displaying custom metadata in Taxonomy Terms Templates
If you need to display custom metadata for each taxonomy term, you will need to create a page for that term at `/content/<TAXONOMY>/<TERM>/_index.md` and add your metadata in its front matter, [as explained in the taxonomies documentation](/content-management/taxonomies/#add-custom-meta-data-to-a-taxonomy-term). Based on the Actors taxonomy example shown there, within your taxonomy terms template, you may access your custom fields by iterating through the variable `.Pages` as such:
```go-html-template
<ul>
{{ range .Pages }}
<li>
<ahref="{{ .Permalink }}">{{ .Title }}</a>
{{ .Params.wikipedia }}
</li>
{{ end }}
</ul>
```
<!-- Begin /taxonomies/ordering/ -->
## Order Taxonomies
Taxonomies can be ordered by either alphabetical key or by the number of content pieces assigned to that key.
When iterating over content within taxonomies, the default sort is the same as that used for section and list pages: first by weight, then by date. This means that if the weights for two pieces of content are the same, then the more recent content will be displayed first.
Weights of zero are thus treated specially: if two pages have unequal weights, and one of them is zero, then the zero-weighted page will always appear after the other one, regardless of the other's weight. Zero weights should thus be used with care: for example, if both positive and negative weights are used to extend a sequence in both directions, a zero-weighted page will appear not in the middle of the list, but at the end.
Content can be assigned weight for each taxonomy that it's assigned to.
```
+++
tags = [ "a", "b", "c" ]
tags_weight = 22
categories = ["d"]
title = "foo"
categories_weight = 44
+++
Front Matter with weighted tags and categories
```
The convention is `taxonomyname_weight`.
In the above example, this piece of content has a weight of 22 which applies to the sorting when rendering the pages assigned to the "a", "b" and "c" values of the 'tag' taxonomy.
It has also been assigned the weight of 44 when rendering the 'd' category.
With this the same piece of content can appear in different positions in different taxonomies.
Currently taxonomies only support the default ordering of content which is weight -> date.
<!-- Begin /taxonomies/templates/ -->
There are two different templates that the use of taxonomies will require you to provide.
Both templates are covered in detail in the templates section.
A [list template](/templates/list/) is any template that will be used to render multiple pieces of content in a single html page. This template will be used to generate all the automatically created taxonomy pages.
A [taxonomy terms template](/templates/terms/) is a template used to
generate the list of terms for a given template.
<!-- Begin /taxonomies/displaying/ -->
There are four common ways you can display the data in your
taxonomies in addition to the automatic taxonomy pages created by hugo
using the [list templates](/templates/list/):
1. For a given piece of content, you can list the terms attached
2. For a given piece of content, you can list other content with the same
term
3. You can list all terms for a taxonomy
4. You can list all taxonomies (with their terms)
## Display a Single Piece of Content's Taxonomies
Within your content templates, you may wish to display the taxonomies that piece of content is assigned to.
Because we are leveraging the front matter system to define taxonomies for content, the taxonomies assigned to each content piece are located in the usual place (i.e., `.Params.<TAXONOMYPLURAL>`).
If you want to list taxonomies inline, you will have to take care of optional plural endings in the title (if multiple taxonomies), as well as commas. Let's say we have a taxonomy "directors" such as `directors: [ "Joel Coen", "Ethan Coen" ]` in the TOML-format front matter.
To list such taxonomies, use the following:
### Example: Comma-delimit Tags in a Single Page Template
```go-html-template
{{ $taxo := "directors" }} <!-- Use the plural form here -->
{{ with .Param $taxo }}
<strong>Director{{ if gt (len .) 1 }}s{{ end }}:</strong>
{{ range $index, $director := . }}
{{- if gt $index 0 }}, {{ end -}}
{{ with $.Site.GetPage (printf "/%s/%s" $taxo $director) -}}
<ahref="{{ .Permalink }}">{{ $director }}</a>
{{- end -}}
{{- end -}}
{{ end }}
```
Alternatively, you may use the [delimit template function][delimit] as a shortcut if the taxonomies should just be listed with a separator. See {{<gh2143>}} on GitHub for discussion.
## List Content with the Same Taxonomy Term
If you are using a taxonomy for something like a series of posts, you can list individual pages associated with the same taxonomy. This is also a quick and dirty method for showing related content:
This would be very useful in a sidebar as “featured content”. You could even have different sections of “featured content” by assigning different terms to the content.
### Example: Grouping "Featured" Content
```go-html-template
<sectionid="menu">
<ul>
{{ range $key, $taxonomy := .Site.Taxonomies.featured }}
If you wish to display the list of all keys for your site's taxonomy, you can retrieve them from the [`.Site` variable][sitevars] available on every page.
This may take the form of a tag cloud, a menu, or simply a list.
The following example displays all terms in a site's tags taxonomy:
### Example: List All Site Tags {#example-list-all-site-tags}
Because taxonomies are lists, the [`.GetPage` function][getpage] can be used to get all the pages associated with a particular taxonomy term using a terse syntax. The following ranges over the full list of tags on your site and links to each of the individual taxonomy pages for each term without having to use the more fragile URL construction of the ["List All Site Tags" example above]({{< relref "#example-list-all-site-tags" >}}):
