MapLibre Tiles (MLT)

The MLT format is mainly inspired by the MVT format specification, but has been redesigned from the ground up to improve the following areas:

Improved compression ratio - up to 6x on large tiles, based on a column oriented layout with (custom) lightweight encodings
Better decoding performance - fast lightweight encodings which can be used in combination with SIMD/vectorization instructions
Support for linear referencing and m-values to efficiently support the upcoming next generation source formats such as Overture Maps (GeoParquet)
Support 3D coordinates, i.e. elevation
Support complex types, including nested properties, lists and maps
Improved processing performance: Based on an in-memory format that can be processed efficiently on the CPU and GPU and loaded directly into GPU buffers partially (like polygons in WebGL) or completely (in case of WebGPU compute shader usage) without additional processing

Caution

This format is still in the active research and development phase and is not ready for production use.

Comparing with MVT

In the following, the size of MLT and MVT files are compared based on a selected set of representative tiles of an OpenMapTiles scheme based OSM dataset. While showing an up to factor 6 reduction in size on large tiles, initial tests also showed equal or mostly even better (between 2x and 3x even without the usage of SIMD) decoding performance compared to MVT in the browser.

Zoom	Tile indices (minX,maxX,minY,maxY)	Tile Size Reduction
2	2, 2, 2, 2	53%
3	4, 4, 5, 5	48%
4		80%
5	16, 17, 20, 21	81%
6	32, 34, 41, 42	76%
7	66, 68, 83, 85	74%
8	132, 135, 170, 171	74%
9	264, 266, 340, 342	68%
10	530, 533, 682, 684	60%
12	2130, 2134, 2733, 2734	65%
13	4264, 4267, 5467, 5468	50%
14	8296, 8300, 10748, 10749	59%

Directory Structure

/spec MLT specification and related documentation
/test Test MVT tiles and the expected MLT conversion results
/java Java encoder for converting MVT to MLT, as well as a decoder parsing MLT to an in-memory representation.
/js Javascript decoder
/rust Rust decoder

Getting Involved

Join the #maplibre-tile-format slack channel at OSMUS: get an invite at https://slack.openstreetmap.us/

License

All project documentation and specification content is licensed under CC0 1.0 Universal - Public Domain Dedication.
All code is dual licensed under Apache License v2.0 and MIT license, at your option.
Tile test data in the /test directory has different licenses depending on the source of that data.

Contribution

Unless you explicitly state otherwise, any code contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions. Similarly, any documentation or specification contributions shall be licensed under CC0 1.0 Universal.