geo-tile — GeoJSON Vector Tiles

A highly efficient JavaScript library for slicing GeoJSON data into vector tiles on the fly, primarily designed to enable rendering and interacting with large geospatial datasets on the browser side (without a server).

Created to power GeoJSON in MapLibre GL JS, but can be useful in other visualization platforms like Leaflet, OpenLayers and d3, as well as Node.js server applications.

Resulting tiles conform to the JSON equivalent of the vector tile specification. To make data rendering and interaction fast, the tiles are simplified, retaining the minimum level of detail appropriate for each zoom level (simplifying shapes, filtering out tiny polygons and polylines).

Demo

Here's geo-tile action in MapLibre GL JS, dynamically loading a 100Mb US zip codes GeoJSON with 5.4 million points:

There's a convenient debug page to test out geo-tile on different data. Just drag any GeoJSON on the page, watching the console.

Usage

// build an initial index of tiles
var tileIndex = geotile(geoJSON);

// request a particular tile
var features = tileIndex.getTile(z, x, y).features;

// show an array of tile coordinates created so far
console.log(tileIndex.tileCoords); // [{z: 0, x: 0, y: 0}, ...]

Options

You can fine-tune the results with an options object, although the defaults are sensible and work well for most use cases.

var tileIndex = geotile(data, {
	maxZoom: 14,  // max zoom to preserve detail on; can't be higher than 24
	tolerance: 3, // simplification tolerance (higher means simpler)
	extent: 4096, // tile extent (both width and height)
	buffer: 64,   // tile buffer on each side
	debug: 0,     // logging level (0 to disable, 1 or 2)
	lineMetrics: false, // whether to enable line metrics tracking for LineString/MultiLineString features
	promoteId: null,    // name of a feature property to promote to feature.id. Cannot be used with `generateId`
	generateId: false,  // whether to generate feature ids. Cannot be used with `promoteId`
	updateable: false,  // whether the tile index can be updated (with the caveat of a stored simplified copy)
	indexMaxZoom: 5,       // max zoom in the initial tile index
	indexMaxPoints: 100000 // max number of points per tile in the index
});

By default, tiles at zoom levels above indexMaxZoom are generated on the fly, but you can pre-generate all possible tiles for data by setting indexMaxZoom and maxZoom to the same value, setting indexMaxPoints to 0, and then accessing the resulting tile coordinates from the tileCoords property of tileIndex.

The promoteId and generateId options ignore existing id values on the feature objects.

Geo-Tile only operates on zoom levels up to 24.

Update

For incremental updates to the tile index, you can use updateData to change features without having to recreate a fresh index. updateData takes a diff object as a parameter with the following properties:

var diff = {
    removeAll: false,             // set to true to clear all features
    remove: ['id1', 'id2'],       // array of feature ids to remove
    add: [feature1, feature2],    // array of GeoJSON features to add
    update: [                     // array of feature update objects
        {
            id: 'feature1',                           // required - id of feature to update
            newGeometry: {type: 'Point', ...},        // new geometry for the feature
            removeAllProperties: false,               // remove all properties
            removeProperties: ['prop1', 'prop2'],     // array of property keys to remove
            addOrUpdateProperties: [                  // array of properties to add/update
                {key: 'name', value: 'New Name'},
                {key: 'population', value: 5000}
            ]
        }
    ]
};

tileIndex.updateData(diff);

All properties in the diff are optional, but at least one operation should be specified. Remove operations are applied before add/update operations.

To use updateData, the index must be created with the updateable: true option.

Install

Install using NPM (npm install geo-tile), then:

// import as a ES module
import geotile from 'geo-tile';

// import from a CDN in the browser:
import geotile from 'https://esm.run/geo-tile';

Or use a browser build directly:

<script src="https://unpkg.com/geo-tile/geo-tile.js"></script>