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.
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Leaflet + Raster Tiles Demo - watch your network request log
Demos require MapLibre GL JS v1.14.1-rc.2 or later
See also:
How To Use
JavaScript
See js/README.md for usage in Leaflet or MapLibre GL JS.
Go
See https://github.com/protomaps/go-pmtiles
Python
pip install pmtiles
pmtiles-convert TILES.mbtiles TILES.pmtiles
pmtiles-convert TILES.pmtiles DIRECTORY
pmtiles-show TILES.pmtiles // see info about a PMTiles directory
pmtiles-serve TILES.pmtiles // start an HTTP server that decodes PMTiles into traditional Z/X/Y paths
See https://github.com/protomaps/PMTiles/tree/master/python/bin for library usage
Specification
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. All integer values are little-endian.
A PMTiles archive is composed of:
- a fixed-size 512,000 byte header section
- Followed by any number of tiles in arbitrary format
- Optionally followed by any number of leaf directories
Header
- The header begins with a 2-byte magic number, "PM"
- Followed by 2 bytes, the PMTiles specification version (currently 2).
- Followed by 4 bytes, the length of metadata (M bytes)
- Followed by 2 bytes, the number of entries in the root directory (N entries)
- Followed by M bytes of metadata, which must be a JSON string with bounds, minzoom and maxzoom properties (new in v2)
- Followed by N * 17 bytes, the root directory.
Directory structure
A directory is a contiguous sequence of 17 byte entries. A directory can have at most 21,845 entries. A directory must be sorted by Z, X and then Y order (new in v2).
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 offset/length points to a leaf directory and not a tile.
- 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 tile, in bytes.
All leaf directory entries follow non-leaf entries. All leaf directories in a single directory must have the same Z value. (new in v2).
Notes
- A full directory of 21,845 entries holds exactly a complete pyramid with 8 levels, or 1+4+16+64+256+1024+4096+16384.
- A PMTiles archive with less than 21,845 tiles should have a root directory and no leaf directories.
- Multiple tile entries can point to the same offset; this is useful for de-duplicating certain tiles, such as an empty "ocean" tile.
- Analogously, multiple leaf directory entries can point to the same offset; this can avoid inefficiently-packed small leaf directories.
- The tentative media type for PMTiles archives is
application/vnd.pmtiles.
Implementation suggestions
- PMTiles is designed to make implementing a writer simple. Reserve 512KB, then write all tiles, recording their entry information; then write all leaf directories; finally, rewind to 0 and write the header.
- The order of tile data in the archive is unspecified; an optimized implementation should arrange tiles on a 2D space-filling curve.
- PMTiles readers should cache directory entries by byte offset, not by Z/X/Y. This means that deduplicated leaf directories result in cache hits.
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.