Indev level format
The .mclevel map format is a new map format, created by Notch. It is based on the NBT format.
The map format is in use since indev version 0.31.
While Alpha (and Infdev) levels use NBT files, they have a very different file format.
For details on the infinite map format, see Alpha Level Format.
[edit] Blocks
The block byte array is used to define the types of blocks that occupy a map. The number of bytes in the array may be calculated by multiplying the dimensions of the map. Y being the up direction rather than Z. For Hex values see Block IDs.
To access a specific block from either the block or data array from XYZ coordinates, use the following formula:
Index = x + (y * Height + z) * Width
[edit] Data
The Data byte array is used for lighting and extra block data. The first 4 bit contains the extra block data (also known as metadata) and the other 4 bits the lighting.
For extended information on block metadata, refer to Data values.
[edit] Lighting
There are 16 levels of lighting for a block ranging from 0x0 (no light) to 0xF (full light).