Flow map drawing layer for deck.gl
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Latest commit 4dcdbf4 Oct 17, 2018

README.md

flowmap.gl

Flow map drawing layer for deck.gl. Can be used for visualizing movement of people (e.g. migration) or objects between geographic locations. The layer is rendered in WebGL and can handle large numbers of flows with a good rendering performance.

Check out the example app and storybook.

Features

Given an array of locations and an array of flows between these locations the layer will do the following:

  • Represent the flows as lines of varying thickness depending on the flow magnitudes
  • The flow lines are sorted so that the larger flows are drawn above
  • GeoJSON geometries of the location areas are rendered as polygons
  • Total incoming and outgoing flows for the locations are calculated and represented as circles of varying sizes.

Location totals

Both the incoming and outgoing totals for the locations are represented. A darker outline means that there are more incoming flows, a lighter outline means that there are more outgoing flows.

For instance, below we compare between the evening and the morning commuting behaviors of a large city:

Difference mode

The layer can be used to show the difference between two moments in time.

Usage

Here's a usage example:

import * as React from 'react';
import DeckGL from 'deck.gl';
import { StaticMap } from 'react-map-gl';
import FlowMapLayer from 'flowmap.gl';

const colors = {
  flows: {
    max: '#137CBD',
  },
  locationAreas: {
    outline: 'rgba(92,112,128,0.5)',
    normal: 'rgba(187,187,187,0.5)',
    selected: 'rgba(217,130,43,0.5)',
  },
};

class MyFlowMap extends React.Component {
  state = { viewState: this.props.initialViewState };
  
  render() {
    const flowMapLayer = new FlowMapLayer({
      id: 'flow-map-layer',
      colors,
      locations: [...],   // array of GeoJSON features of location areas
      flows: [...],       // array of Flow objects
      getLocationId: l => l.id,
      getLocationCentroid: l => l.properties.centroid,
      getFlowOriginId: f => f.origin,
      getFlowDestId: f => f.dest,
      getFlowMagnitude: f => f.count,
      showTotals: true,
      showLocationAreas: true,
      locationCircleSize: 3,
      varyFlowColorByMagnitude: true,
    });
    
    return (
      <DeckGL 
        layers={[flowMapLayer]}
        initialViewState={this.state.viewState}
        controller={true}
        onViewStateChange={({ viewState }) => this.setState({ viewState })}
        children={({ width, height, viewState }) => (
          <StaticMap mapboxApiAccessToken={mapboxAccessToken} width={width} height={height} viewState={viewState} />
        )}
      />
    );
  }  
}

The full list of supported props:

interface Props {
  id: string;
  colors: Colors | DiffColors;
  locations: Locations;
  flows: Flow[];
  fp64?: boolean;
  onClick?: PickingHandler<FlowLayerPickingInfo>;
  onHover?: PickingHandler<FlowLayerPickingInfo>;
  getLocationId?: LocationAccessor<string>;
  getLocationCentroid?: LocationAccessor<[number, number]>;
  getLocationTotalIn?: LocationAccessor<number>;
  getLocationTotalOut?: LocationAccessor<number>;
  getFlowOriginId?: FlowAccessor<string>;
  getFlowDestId?: FlowAccessor<string>;
  getFlowMagnitude?: FlowAccessor<number>;
  showTotals?: boolean;
  locationCircleSize?: number;
  showLocationAreas?: boolean;
  varyFlowColorByMagnitude?: boolean;
  selectedLocationIds?: string[];
  highlightedLocationId?: string;
  highlightedFlow?: Flow;
  visible?: boolean;
  opacity?: number;
  pickable?: boolean;
  fp64?: boolean;
  updateTriggers?: UpdateTriggers;
}

Here's the code for the example app and a more complex interactive example.

Developing

Create an .env file in the project root containing one line:

MapboxAccessToken=<your-mapbox-access-token>

Then, run:

npm install
npm start
open http://localhost:6006 to open storybook

Acknowledgements

Many thanks to Philippe Voinov for his help with the first version of the FlowLinesLayer.

License

flowmap.gl Copyright 2018 Teralytics

This product includes software developed at The Apache Software Foundation (http://www.apache.org/).

Portions of this software were developed at Teralytics (http://www.teralytics.net)