# Tree map view

The Tree map view is new in IceCat 48.

The Tree map view provides a visual representation of the snapshot, that
helps you quickly get an idea of which objects are using the most
memory.

A treemap displays [\"hierarchical (tree-structured) data as a set of
nested rectangles\"](https://en.wikipedia.org/wiki/Treemapping). The
size of the rectangles corresponds to some quantitative aspect of the
data.

For the treemaps shown in the Memory tool, things on the heap are
divided at the top level into four categories:

-   **objects**: JavaScript and DOM objects, such as `Function`,
    `Object`, or `Array`, and DOM types like `Window` and
    `HTMLDivElement`.
-   **scripts**: JavaScript sources loaded by the page.
-   **strings**
-   **other**: this includes internal
    [SpiderMonkey](https://developer.mozilla.org/en-US/docs/Tools/Tools_Toolbox#settings/en-US/docs/Mozilla/Projects/SpiderMonkey) objects.

Each category is represented with a rectangle, and the size of the
rectangle corresponds to the proportion of the heap occupied by items in
that category. This means you can quickly get an idea of roughly what
sorts of things allocated by your site are using the most memory.

Within top-level categories:

-   **objects** is further divided by the object's type.
-   **scripts** is further subdivided by the script's origin. It also
    includes a separate rectangle for code that can't be correlated
    with a file, such as JIT-optimized code.
-   **other** is further subdivided by the object's type.

Here are some example snapshots, as they appear in the Tree map view:

![](../img/treemap-domnodes.png)

This treemap is from the [DOM allocation
example](DOM_allocation_example.md), which runs a
script that creates a large number of DOM nodes (200 `HTMLDivElement`
objects and 4000 `HTMLSpanElement` objects). You can see how almost all
the heap usage is from the `HTMLSpanElement` objects that it creates.

![](../img/treemap-monsters.png)

This treemap is from the [monster allocation
example](monster_example.md), which creates three
arrays, each containing 5000 monsters, each monster having a
randomly-generated name. You can see that most of the heap is occupied
by the strings used for the monsters' names, and the objects used to
contain the monsters' other attributes.

![](../img/treemap-bbc.png)

This treemap is from <http://www.bbc.com/>, and is probably more
representative of real life than the examples. You can see the much
larger proportion of the heap occupied by scripts, that are loaded from
a large number of origins.
