# Networks and Trees

## Networks

Network data is data that describes relations between objects.

Other types of data discussed so far (tabular data, temporal data, geographical data) have objects and values. Network data also has **relationships**, along with objects and values.

Objects are represented using **nodes** and relationships are denoted using **links**/**edges**. Values can be associated with both nodes and links.

## Trees

Trees are used to represent hierarchical data. This is why they are also called **hierarchies**.

Some common examples of such data include:

* file systems
* evolutionary trees (phylogenetic trees)
* geographical data
* temporal data
* organizational structures
* language structures

General structure of a tree:

![](https://192301203-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M5-0RG_uqhxyMNjpMUW%2F-M5-0SvQ45Rarxg8L2lA%2F-M5-0VEGnfb6TRwGT8cE%2Ftree.png?generation=1586990823757482\&alt=media)

Note that every child can have exactly one parent node.

The following sections discuss the visualization of networks and trees.