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 - watch your network request log

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.

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