Using Sources

loaders.gl provides a number of Source exports that support multi-step data loading. Sources are different from loaders, in that the latter are designed for "one-shot" atomic or streaming loads of data, while a Source can be thought of as a multi-step or multi-resource loader. (A source can use one or more loaders internally).

Sources are designed encapsulates the following data access models:

Data Access Model	Description
*web service	Interact with a web service that returns data assets for different regions etc.
cloud storage	Read static assets as-needed from large cloud-native file formats
archive files	Read individual assets from a (very large) multi-asset archive files.
dynamic data generation	Generate data (tiles, images etc) dynamically based on application requests.

Source

A Source object provides information for creating a DataSource

DataSource Interfaces

A DateSource instance provides methods to query metadata, and to query data for specific geospatial areas.

A DataSource can (and sometimes must) expose a completely unique API. However a big advantages comes when a DataSource conforms to an existing Source interface.

This means that applications written against that interface can now support the new source without any changes to existing logic.

Source Interface	Data access model	Examples
ImageSource	Loads image covering a region	WMSSource, _ArcGISImageServerSource
VectorSource	Load "features" in a region	WFS (N/A), ArcGIS FeatureServer
ImageTileSource	Load image covering a specific tile index	WMTS (N/A)
VectorTileSource	Load "features" in a specific tile index	Mapbox Vector Tiles, PMTilesSource

Metadata

A DateSource instance provides methods to query metadata: await dataSource.getMetadata().

Adapter Sources

While most Source implementations provide an interface for interacting with a specific web service or cloud archive file format (e.g. PMtilesSource), it is also possible to create adapters:

• that provide a Source interface to local data (TableTileSource)
• that adapts one type of Source to another (e.g. ImageTileSource calling an ImageSource to generate each tile).

Source auto-selection

Just like the appropriate loader can be selected automatically from a list of Loader objects, createDataSource() and selectSource() accept a list of Source objects and attempt to select the correct one based on URL pattern matching, root file first bytes etc.

Creating new Sources

Just like applications can create their own own loaders, apps can also create (and potentially contribute) their own sources and use them with loaders.gl, as long as they follow the required interfaces (e.g, every source instance must inherit from DataSource).

Example

import {TableTileSource} from '@loaders.gl/mvt';
import {GeoJSONLoader} from '@loaders.gl/json';

// build an initial index of tiles. Convieniently, 
const tileSource = new TableTileSource(load(url, GeoJSONLoader));
// request a particular tile
const features = tileSource.getTile(z, x, y).features;