MapLibre Tiles (MLT)

The MapLibre Tile specification is mainly inspired by the Mapbox Vector Tile (MVT) specification, but has been redesigned from the ground up to address the challenges of rapidly growing geospatial data volumes and complex next-generation geospatial source formats as well as to leverage the capabilities of modern hardware and APIs. MLT is specifically designed for modern and next generation graphics APIs to enable high-performance processing and rendering of large (planet-scale) 2D and 2.5 basemaps. In particular, MLT offers the following features:

Improved compression ratio: up to 6x on large tiles, based on a column oriented layout with recursively applied (custom) lightweight encodings. This leads to reduced latency, storage, and egress costs and, in particular, improved cache utilization
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 storage and in-memory formats that are specifically designed for modern GL APIs, allowing for efficient processing on both CPU and GPU. The formats are designed to be loaded into GPU buffers with little or no additional processing

📝 For a more in-depth exploration of MLT have a look at the following slides or watch this talk.

[!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/

Development

This project is easier to develop with just, a modern alternative to make.
To get a list of available commands, run just.
To run tests, use just test.

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.

maplibre / maplibre-tile-spec

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