Terrain & large worlds
World Partition Cell & Loading Range Planner
Direct answer
World Partition divides a map into runtime grid cells and loads cells intersecting a radius around each streaming source. A 4x4 km world using 256 m cells contains 256 cells. With a 768 m loading range, roughly 44 cells intersect one circular source before HLODs, actor bundling and implementation overhead.
Measure this from your project; the default is only a planning placeholder.
Result
- Approximate cells intersecting one source
- —
- Whole-world grid
- —
- Total world cells
- —
- Approximate loaded cell area
- —km2
- Estimated resident data for all sources
- —GiB
- Loading range in cell widths
- —
- Travel time across loading radius
- —s
- Streaming lead check
- —
Method & assumptions
How this is worked out
Whole-world cell count rounds each map axis up to a complete cell. The loaded-cell estimate expands the circular loading radius by half a cell diagonal, then divides that circle by cell area. This approximates cells that intersect the source shape rather than only cells whose centre lies inside it.
Estimated resident data multiplies intersecting cells, average measured cell size and simultaneous sources. Overlapping sources are intentionally not deduplicated, making this a conservative planning number.
Streaming lead time is loading range divided by maximum travel speed. It is not an I/O prediction; it tells you how long content has to become ready after entering the edge of the loading radius.
How to interpret the planner
| Signal | Prefer lower | Prefer higher |
|---|---|---|
| Cell size | Granular streaming and rebuilds | Fewer cells and less management overhead |
| Loading range | Lower memory residency | More time to stream and fewer visible pop-ins |
| Cell memory | Lighter content and HLODs | Denser actors, textures and collision |
| Lead time | Fast storage and simple cells | Slow storage or high-speed traversal |
Epic recommends avoiding multiple runtime grids unless a project has measured evidence that they help. Profile actual cells because actor references can bundle content across cell boundaries.
Questions
What is a World Partition loading range?
It is the radius around a streaming source within which runtime grid cells are loaded. Player Controllers can act as sources, and custom streaming source components can prepare teleport destinations or other important regions.
Does the loaded-cell number equal exact runtime residency?
No. It is a geometric estimate. Source shapes, grid alignment, overlapping sources, actor references, Data Layers, HLODs and cell state can all change the exact set. Use it for planning, then verify with runtime streaming debug views.
How should I choose cell size?
Start from the scale at which content should stream independently. Smaller cells give finer control but create more cells and management overhead. Larger cells reduce bookkeeping but can load much more content than the player currently needs.
Sources and assumptions
Sources define the engine settings or mathematical model. Project-specific performance and final playability still need measurement in the target build.