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Basic Concepts of Map Implementation in ECharts

The map implementation in ECharts primarily relies on geographic coordinate systems and map series. The geographic coordinate system is used to map geographic data onto a two-dimensional plane, while the map series is responsible for rendering the actual map graphics. ECharts supports various map data formats, including GeoJSON and TopoJSON, and also provides simplified built-in data for maps of China and the world.

The core of map implementation lies in coordinate system configuration and data binding. The geographic coordinate system requires specifying a map projection method, with common options being 'mercator', 'equalEarth', etc. Data binding involves associating geographic features with numerical values to create visual effects.

option = {
  geo: {
    map: 'china',
    roam: true
  },
  series: [{
    type: 'map',
    map: 'china',
    data: [
      {name: 'Beijing', value: 100},
      {name: 'Shanghai', value: 200}
    ]
  }]
};

Registering and Using Map Data

Before using a map, the map data must be registered. ECharts provides two methods: directly importing JSON files or using online resources. For the China map, the built-in 'china' identifier can be used directly, but more complex maps require manual registration.

// Example of registering map data
$.get('map-data/china.json', function(chinaJson) {
  echarts.registerMap('china', chinaJson);
  
  var chart = echarts.init(document.getElementById('main'));
  chart.setOption({
    series: [{
      type: 'map',
      map: 'china'
    }]
  });
});

For provincial-level maps, more detailed data is required:

// Registering a Zhejiang Province map
$.get('map-data/zhejiang.json', function(zjJson) {
  echarts.registerMap('zhejiang', zjJson);
  
  var chart = echarts.init(document.getElementById('main'));
  chart.setOption({
    series: [{
      type: 'map',
      map: 'zhejiang',
      data: [
        {name: 'Hangzhou', value: 583},
        {name: 'Ningbo', value: 432}
      ]
    }]
  });
});

Visual Mapping for Maps

Visual mapping is the process of converting data values into visual elements (e.g., color, size). ECharts provides the visualMap component to achieve this, supporting both continuous and piecewise visual mapping methods.

Example of continuous visual mapping:

option = {
  visualMap: {
    min: 0,
    max: 1000,
    text: ['High', 'Low'],
    realtime: false,
    calculable: true,
    inRange: {
      color: ['#50a3ba', '#eac736', '#d94e5d']
    }
  },
  series: [{
    type: 'map',
    map: 'china',
    data: [
      {name: 'Guangdong', value: 923},
      {name: 'Sichuan', value: 614}
    ]
  }]
};

Example of piecewise visual mapping:

option = {
  visualMap: {
    type: 'piecewise',
    pieces: [
      {min: 1000},
      {min: 500, max: 999},
      {min: 100, max: 499},
      {max: 99}
    ],
    inRange: {
      color: ['#00467F', '#A5CC82']
    }
  },
  series: [{
    type: 'map',
    map: 'china',
    data: [
      {name: 'Jiangsu', value: 872},
      {name: 'Henan', value: 453}
    ]
  }]
};

Interactive Features of Maps

ECharts maps support rich interactive features, including zooming, panning, and region highlighting. These features are implemented by configuring properties such as roam and emphasis.

Basic interaction configuration:

option = {
  series: [{
    type: 'map',
    map: 'china',
    roam: true,  // Enable zooming and panning
    emphasis: {  // Highlight style
      itemStyle: {
        areaColor: '#f4cccc'
      },
      label: {
        show: true
      }
    }
  }]
};

Adding click events:

myChart.on('click', function(params) {
  console.log(params.name);
});

Combining Heatmaps and Scatter Plots

Maps can be combined with other chart types to create richer visualizations. Heatmaps and scatter plots are common combinations.

Example of a map heatmap:

option = {
  tooltip: {},
  visualMap: {
    min: 0,
    max: 10,
    calculable: true,
    inRange: {
      color: ['#50a3ba', '#eac736', '#d94e5d']
    }
  },
  geo: {
    map: 'china',
    roam: true
  },
  series: [{
    type: 'heatmap',
    coordinateSystem: 'geo',
    data: [
      {name: 'Beijing', value: [116.46, 39.92, 9]},
      {name: 'Shanghai', value: [121.48, 31.22, 7]}
    ],
    pointSize: 10,
    blurSize: 15
  }]
};

Example of a map scatter plot:

option = {
  geo: {
    map: 'china',
    roam: true
  },
  series: [{
    type: 'scatter',
    coordinateSystem: 'geo',
    symbolSize: 12,
    data: [
      {name: 'Wuhan', value: [114.31, 30.52, 195]},
      {name: 'Chengdu', value: [104.06, 30.67, 123]}
    ],
    label: {
      show: false
    },
    itemStyle: {
      color: '#dd6b66'
    }
  }]
};

Customizing Map Styles

ECharts allows deep customization of map styles, including region colors, border styles, and label display. These styles can be configured in itemStyle and label.

Basic style configuration:

option = {
  series: [{
    type: 'map',
    map: 'china',
    itemStyle: {
      areaColor: '#e6f7ff',
      borderColor: '#1890ff',
      borderWidth: 1
    },
    label: {
      color: '#333',
      fontSize: 12
    },
    emphasis: {
      itemStyle: {
        areaColor: '#1890ff'
      },
      label: {
        color: '#fff'
      }
    }
  }]
};

Using an image as a region background:

option = {
  series: [{
    type: 'map',
    map: 'china',
    itemStyle: {
      areaColor: {
        image: 'texture.jpg',
        repeat: 'repeat'
      }
    }
  }]
};

Linking Multiple Maps

ECharts supports linking multiple map instances, which can be achieved using the connect property. This is particularly useful for displaying maps at different levels (e.g., country-province).

Example of linked maps:

// Initialize two chart instances
var chart1 = echarts.init(document.getElementById('main1'));
var chart2 = echarts.init(document.getElementById('main2'));

// Set options for the country map
chart1.setOption({
  series: [{
    type: 'map',
    map: 'china'
  }]
});

// Set options for the provincial map
chart2.setOption({
  series: [{
    type: 'map',
    map: 'zhejiang'
  }]
});

// Link the two charts
echarts.connect([chart1, chart2]);

Dynamic Data Updates

Map data can be updated dynamically to achieve real-time visualization effects. This is done using the setOption method, which allows updating only the data portion without affecting other configurations.

Example of dynamic updates:

// Initial setup
var option = {
  series: [{
    type: 'map',
    map: 'china',
    data: []
  }]
};

// Generate random data and update
function updateData() {
  var data = [];
  var cities = ['Beijing', 'Shanghai', 'Guangzhou', 'Shenzhen', 'Chengdu'];
  cities.forEach(function(city) {
    data.push({
      name: city,
      value: Math.round(Math.random() * 1000)
    });
  });
  
  myChart.setOption({
    series: [{
      data: data
    }]
  });
}

// Update data every 2 seconds
setInterval(updateData, 2000);

Combining Maps with Timelines

Combining maps with timelines can visualize data changes over time. This requires using the timeline component and multiple options configurations.

Example of a timeline map:

option = {
  baseOption: {
    timeline: {
      axisType: 'category',
      autoPlay: true,
      data: ['2020', '2021', '2022']
    },
    series: [{
      type: 'map',
      map: 'china'
    }]
  },
  options: [
    {
      title: {text: '2020 Data'},
      series: [{
        data: [
          {name: 'Beijing', value: 523},
          {name: 'Shanghai', value: 432}
        ]
      }]
    },
    {
      title: {text: '2021 Data'},
      series: [{
        data: [
          {name: 'Beijing', value: 687},
          {name: 'Shanghai', value: 521}
        ]
      }]
    },
    {
      title: {text: '2022 Data'},
      series: [{
        data: [
          {name: 'Beijing', value: 754},
          {name: 'Shanghai', value: 632}
        ]
      }]
    }
  ]
};

3D Map Implementation

The ECharts GL extension supports 3D map visualization, enabling more立体感 (three-dimensional) map effects. 3D maps require the additional ECharts GL library.

Basic example of a 3D map:

option = {
  backgroundColor: '#000',
  geo3D: {
    map: 'china',
    regionHeight: 2,
    itemStyle: {
      color: '#1a1a1a',
      opacity: 1,
      borderWidth: 0.5,
      borderColor: '#404a59'
    },
    viewControl: {
      distance: 120,
      alpha: 30,
      beta: 30
    }
  }
};

3D map with height:

option = {
  geo3D: {
    map: 'china',
    shading: 'realistic',
    realisticMaterial: {
      roughness: 0.8,
      metalness: 0
    },
    postEffect: {
      enable: true,
      SSAO: {
        enable: true,
        radius: 2,
        intensity: 1.5
      }
    },
    light: {
      main: {
        intensity: 2,
        shadow: true,
        shadowQuality: 'high',
        alpha: 30,
        beta: 40
      },
      ambient: {
        intensity: 0
      }
    },
    data: [
      {name: 'Tibet', value: 300},
      {name: 'Xinjiang', value: 200},
      {name: 'Jiangsu', value: 50}
    ]
  }
};

Custom Projection Methods

ECharts supports custom map projection methods, which is useful for special requirements or non-standard maps. This can be achieved via the project configuration.

Example of custom projection:

option = {
  geo: {
    map: 'china',
    projection: {
      project: function(point) {
        return [
          point[0] / 180 * Math.PI,
          -Math.log(Math.tan((Math.PI / 2 + point[1] / 180 * Math.PI) / 2))
        ];
      },
      unproject: function(point) {
        return [
          point[0] * 180 / Math.PI,
          2 * 180 / Math.PI * Math.atan(Math.exp(point[1])) - 90
        ];
      }
    }
  }
};

Combining Maps with Other Charts

Maps can be combined with other chart types in the same coordinate system to create complex visualizations. Common examples include overlaying bar charts or line charts on maps.

Example of combining a map with a bar chart:

option = {
  geo: {
    map: 'china',
    roam: true
  },
  series: [
    {
      type: 'map',
      map: 'china',
      data: [
        {name: 'Beijing', value: 100},
        {name: 'Shanghai', value: 200}
      ]
    },
    {
      type: 'bar3D',
      coordinateSystem: 'geo',
      barSize: 0.5,
      shading: 'realistic',
      data: [
        {name: 'Beijing', value: [116.46, 39.92, 100]},
        {name: 'Shanghai', value: [121.48, 31.22, 200]}
      ],
      emphasis: {
        itemStyle: {
          color: '#dd6b66'
        }
      }
    }
  ]
};

Map Boundaries and Markers

In addition to region filling, maps also support custom boundary lines and markers. These are configured via markPoint and markLine.

Example of markers and lines:

option = {
  series: [{
    type: 'map',
    map: 'china',
    markPoint: {
      symbol: 'pin',
      symbolSize: 50,
      data: [
        {name: 'Marker 1', coord: [116.46, 39.92]},
        {name: 'Marker 2', coord: [121.48, 31.22]}
      ]
    },
    markLine: {
      silent: true,
      data: [{
        coord: [[116.46, 39.92], [121.48, 31.22]]
      }],
      lineStyle: {
        color: '#f00',
        width: 2
      }
    }
  }]
};

Performance Optimization Tips

When dealing with large map datasets, performance optimization becomes crucial. Here are some practical tips:

1. Simplify map data: Use simplified GeoJSON files to reduce vertex count.
2. Use visual mapping wisely: Avoid overly complex visual mapping calculations.
3. Render on demand: For large-area maps, display an overview first and load details as needed.

Example of simplified data:

// Using simplified China map data
$.get('map-data/china-simple.json', function(chinaJson) {
  echarts.registerMap('china-simple', chinaJson);
  
  var chart = echarts.init(document.getElementById('main'));
  chart.setOption({
    series: [{
      type: 'map',
      map: 'china-simple'
    }]
  });
});

Common Issues and Solutions

In practice, various issues may arise. Here are some common problems and their solutions:

1. Map not displaying: Check if the map data is registered correctly and ensure the JSON file path is accurate.
2. Region colors not changing: Verify that the visualMap configuration is correct and the data format meets requirements.
3. Label overlap: Adjust the show, position, and other properties of label.

Debugging example:

// Debugging map data loading
$.get('map-data/china.json')
  .done(function(data) {
    console.log('Map data loaded successfully', data);
    echarts.registerMap('china', data);
  })
  .fail(function(error) {
    console.error('Map data loading failed', error);
  });