# Feature types

OS Open Built Up Areas is classified into three feature types: Built Up Areas, Built Up Extents, and Non Built Up Extents. The attributes associated with these feature types are listed below along with a brief description of their data properties.

<figure><img src="https://1897589978-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FcNpJpLP8RROUaWVQo5ea%2Fuploads%2FZQOGQFUY0xqdUQpxoHZ9%2F4.png?alt=media" alt="Unified Modeling Language (UML) diagram showing the data structure of OS Open Built Up Areas"><figcaption><p>Unified Modeling Language (UML) diagram showing the data structure of OS Open Built Up Areas</p></figcaption></figure>

### **Name and Definition**

The name of the attribute and what it is describing.

### **Data type**

The nature of the attribute, for example a numeric value or a code list value.

### **Size**

The length of the attribute provided (optional).

### **Multiplicity**

Describes how many times this element is expected to be populated in the data. An attribute may be optional or mandatory within the product. These are denoted by:

* ‘1’ – there must be a value.
* ‘0..1’ – population is optional but a maximum of one attribute will be returned These values may be used in combination.