# Merge Part Occurrences by Regions

> Use this feature to merge part occurrences together based on their physical proximity in the scene, meaning by region.

API functions:

* [scene.mergePartOccurrencesByRegions](/asset-transformer-sdk/2026.4/api/python/scene_functions.md#mergepartoccurrencesbyregions)
* [scene.getClusters](/asset-transformer-sdk/2026.4/api/python/scene_functions.md#getclusters)

![Image](/api/media?file=/asset-transformer-sdk/media/images/merge-by-regions/algo-merge-by-regions2.png)

> **Note:**
>
> Use [scene.getClusters](/asset-transformer-sdk/2026.4/api/python/scene_functions.md#getclusters) to get part occurrences based on their physical proximity in the scene **without merging them**.

This function fits particularly with large AEC models, coming from Revit, AutoCAD, Navisworks or RVM files.

![Image](/api/media?file=/asset-transformer-sdk/media/images/merge-by-regions/algo-merge-by-regions.gif)

Indeed, if the model can be merged this function will greatly help with performances:

* **merging** lowers the number of draw calls
* **by regions** lets still benefit from [frustrum culling](https://docs.unity3d.com/Manual/OcclusionCulling.html) (contrary to other `Merge` functions that do not merge by location/region but by hierarchy)

This is particularly interesting with large AEC buildings where the model is the environment. If the user is at the center of the building and looking one way, the parts behind him won't be drawn. It would have been drawn if the whole model was merged:

| Full Merge                                                                                    | Merge by Regions                                                                            |
| --------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------- |
| ![Image](/api/media?file=/asset-transformer-sdk/media/images/merge-by-regions/nofrustrum.png) | ![Image](/api/media?file=/asset-transformer-sdk/media/images/merge-by-regions/frustrum.png) |