# Region
One 64 by 64 tile square of the world, expanded from the cache into the per-plane arrays the map
renderer walks: heights, settings, ground overlays and underlays, and the objects standing on it.


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## Region._InitArrays
```pascal
procedure TRegion._InitArrays();
```
Allocates the region's per-plane tile arrays - 4 planes of 64 by 64, indexed `[z, x, y]`.


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## Region.Create
```pascal
function TRegion.Create(id: Integer): TRegion; static;
function TRegion.Create(x, y: Integer): TRegion; static; overload;
```
An empty region at the given position, addressed either by its packed id or by its region
coordinates.

A region id packs its x into the high byte and its y into the low one, and each region covers 64
by 64 world tiles starting at `BaseX, BaseY`. The tile arrays are allocated but hold nothing
until {ref}`TRegion.LoadTerrain` fills them.


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## Region.LoadTerrain
```pascal
procedure TRegion.LoadTerrain(constref map: TMapDefinition);
```
Expands a decoded {ref}`TMapDefinition` into the region's per-plane tile arrays.

A ground tile with no stored height falls back to the procedural terrain height, which depends
only on the tile's world x and y, so the whole region's worth is built in one pass the first time
any tile asks for it. A tile on a higher plane with no stored height sits 240 above the one below
it, the way the client does it.


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## Region.LoadLocations
```pascal
procedure TRegion.LoadLocations(constref locs: TLocationsDefinition);
```
Takes the region's object placements from a decoded {ref}`TLocationsDefinition`, converting each
one from a position within the region to a world coordinate.


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## Region.GetOverlayID
```pascal
function TRegion.GetOverlayID(z, x, y: Integer): Integer;
```
The ground overlay of one tile, or `0` if it has none.

The stored value keeps a flag in its top bit, which is masked off here.


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## Region.GetUnderlayID
```pascal
function TRegion.GetUnderlayID(z, x, y: Integer): Integer;
```
The ground underlay of one tile, or `0` if it has none, with the same flag bit masked off that
{ref}`TRegion.GetOverlayID` masks.