Dynamic feature charting with Chart.js
Plot feature attributes on a dynamic chart that updates as users pan and zoom, and respond to chart interactions by modifying feature layer contents. This demo relies on Chart.js to render an interactive scatterplot.
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<title>Dynamic feature charting with Chart.js</title>
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<style>
body { margin:0; padding:0; }
#map { position: absolute; top:0; bottom:0; right:0; left:0; }
</style>
</head>
<body>
<!-- Load Chart.js from CDN -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.3/Chart.min.js"></script>
<style>
.chart-container {
height: 245px;
width: 245px;
}
#info-pane {
position: absolute;
top: 10px;
right: 10px;
z-index: 400;
padding: 1em;
background: white;
}
</style>
<div id="map"></div>
<div id="info-pane" class="leaflet-bar chart-container">
<canvas id="chartCanvas"></canvas>
</div>
<script>
// STEP 1: MAKE A MAP AND ADD LAYERS
var map = L.map('map').setView([45.526, -122.667], 13);
L.esri.basemapLayer('Topographic').addTo(map);
// create and add a feature layer
// features from this layer will appear in the Chart.js scatterplot
var treesFeatureLayer = L.esri.featureLayer({
url: 'https://services.arcgis.com/rOo16HdIMeOBI4Mb/arcgis/rest/services/Heritage_Trees_Portland/FeatureServer/0',
});
treesFeatureLayer.addTo(map);
// STEP 2: DEFINE A CHART
// this is a static scatterplot chart definition for now, but it will
// soon become dynamic by responding to map and feature layer events
var initialChartData = {
datasets: [{
label: 'Portland Heritage Trees',
// the data values are empty at this moment
// and will be updated dynamically below
data: []
}]
};
var chartOptions = {
scales: {
xAxes: [{
scaleLabel: {
display: true,
labelString: 'tree diameter'
},
ticks: {
beginAtZero: true,
max: 250,
stepSize: 50
}
}],
yAxes: [{
scaleLabel: {
display: true,
labelString: 'tree height'
},
ticks: {
beginAtZero: true,
max: 250,
stepSize: 50
}
}]
},
maintainAspectRatio: false,
// turn off animations during chart data updates
animation: {
duration: 0,
},
// see STEP 4 below
onHover: handleChartHover
};
var chart = new Chart('chartCanvas', {
type: 'scatter',
data: initialChartData,
options: chartOptions
});
// STEP 3: MAKE THE CHART DYNAMIC BY ESTABLISHING MAP-TO-CHART COMMUNICATION
// show in the scatterplot only the features in the map's current extent
// by handling several events from both the map and feature layer
map.on('zoom move', updateChart);
treesFeatureLayer.on('load', updateChart);
function updateChart() {
// reformat the features' attributes of interest into
// the data array format required by the Chart.js scatterplot
var scatterPlotDataArray = [];
treesFeatureLayer.eachActiveFeature(function(e) {
// loop over each active feature in the map extent and
// push an object into the scatterPlotDataArray in this format:
// {
// x: diameter attribute value,
// y: height attribute value,
// featureId: unique ID for chart-to-map communication in STEP 4
// }
scatterPlotDataArray.push({
x: e.feature.properties.DIAMETER,
y: e.feature.properties.HEIGHT,
featureId: e.feature.id
});
});
// assign the new scatterPlotDataArray to the chart's data property
chart.data.datasets[0].data = scatterPlotDataArray;
// finally, instruct the chart to re-draw itself with the new data
chart.update();
}
// STEP 4 (OPTIONAL): ESTABLISH CHART-TO-MAP COMMUNICATION
// up until now the map and feature layer inform the chart what to render,
// but interactions with the chart can also influence the map contents
function handleChartHover(e) {
var chartHoverData = chart.getElementsAtEvent(e);
if (!chartHoverData.length) {
// if there were no data elements found when hovering over the chart,
// reset any previous styling overrides and return
treesFeatureLayer.eachFeature(function(e) {
e.setOpacity(1);
e.setZIndexOffset(0);
});
return;
}
// otherwise, bring attention to the features on the map
// that are currently being hovered over in the chart
var hoverFeatureIds = chartHoverData.map(function(datum) {
return chart.data.datasets[0].data[datum._index].featureId;
});
treesFeatureLayer.eachFeature(function(e, idx) {
if (
hoverFeatureIds.indexOf(e.feature.id) > -1
) {
e.setOpacity(1);
e.setZIndexOffset(10000);
} else {
e.setOpacity(0.1);
}
});
}
</script>
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