# PMTiles

PMTiles is a single-file archive format for tiled data. A PMTiles archive can be hosted on a commodity storage platform such as S3, and enables low-cost, zero-maintenance map applications that are "serverless" - free of a custom tile backend or third party provider.

[Demo](https://protomaps.github.io/PMTiles/examples/leaflet.html) - watch your network request log

See also:
* [Cloud Optimized GeoTIFFs](https://www.cogeo.org)

## Specification

A detailed specification is forthcoming. PMTiles is a binary serialization format designed for two main access patterns: over the network, via HTTP 1.1 Byte Serving (`Range:` requests), or via memory-mapped files on disk.

### Design considerations
* Directories are recursive, with a maximum of 21,845 entries per directory.
* Deduplication of tile data is handled by multiple entries pointing to the same offset in the archive.

### Details
* The first 512 kilobytes of a PMTiles archive are reserved, and contain the headers as well as a root directory.
* All integer values are little-endian.
* The headers begin with a magic number, "PM"
* 2 bytes: which specify the PMTiles specification version, right now always 1.
* 4 bytes: the length of metadata (M bytes)
* 2 bytes: the number of entries in the root directory (N)
* M bytes: the metadata, by convention a JSON object.
* N * 17 bytes: the root directory.

### Directory structure

A directory is a sequence of 17 byte entries. An entry consists of:
* 1 byte: the zoom level (Z) of the entry, with the top bit set to 1 instead of 0 to indicate the data is a child directory, not data.
* 3 bytes: the X (column) of the entry.
* 3 bytes: the Y (row) of the entry.
* 6 bytes: the offset of where the tile begins in the archive.
* 4 bytes: the length of the data.

## License

The reference implementations of PMTiles are published under the BSD 3-Clause License. The PMTiles specification itself is public domain, or under a CC0 license where applicable.