Create a Gradient Line Using an Expression
The line-gradient paint property in Maptoolkit Maps JS uses an interpolate expression to map positions along a line (from 0 at the start to 1 at the end) to color values. The source must have lineMetrics: true enabled for the gradient to work correctly. Use this to color-code routes by speed, elevation, or any continuous metric that varies along a path.
const API_KEY = 'YOUR_API_KEY';
const map = new maptoolkit.Map({
container: 'map',
apiKey: API_KEY,
style: `https://styles.maptoolkit.net/maptoolkit/maptoolkit.summer.json?api_key=${API_KEY}`,
center: [-77.035, 38.875],
zoom: 12,
attributionControl: { compact: false }
});
map.addControl(new maptoolkit.NavigationControl(), 'top-right');
const geojson = {
type: 'FeatureCollection',
features: [{
type: 'Feature',
properties: {},
geometry: {
type: 'LineString',
coordinates: [
[-77.044211, 38.852924],
[-77.045659, 38.860158],
[-77.044232, 38.862326],
[-77.040879, 38.865454],
[-77.039936, 38.867698],
[-77.040338, 38.86943],
[-77.04264, 38.872528],
[-77.03696, 38.878424],
[-77.032309, 38.87937],
[-77.030056, 38.880945],
[-77.027645, 38.881779],
[-77.026946, 38.882645],
[-77.026942, 38.885502],
[-77.028054, 38.887449],
[-77.02806, 38.892088],
[-77.03364, 38.892108],
[-77.033643, 38.899926]
]
}
}]
};
map.on('load', () => {
map.addSource('line', {
type: 'geojson',
lineMetrics: true,
data: geojson
});
map.addLayer({
id: 'line',
type: 'line',
source: 'line',
paint: {
'line-color': 'red',
'line-width': 14,
'line-gradient': [
'interpolate', ['linear'], ['line-progress'],
0, 'blue',
0.1, 'royalblue',
0.3, 'cyan',
0.5, 'lime',
0.7, 'yellow',
1, 'red'
]
},
layout: {
'line-cap': 'round',
'line-join': 'round'
}
});
});<!DOCTYPE html>
<html lang="en">
<head>
<title>Create a Gradient Line Using an Expression - Maptoolkit Maps JS</title>
<meta property="og:description" content="Style a line with a color gradient using a line-gradient expression." />
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<script src="https://unpkg.com/@maptoolkit/[email protected]/dist/maptoolkit.js"></script>
<link rel="stylesheet" href="https://unpkg.com/@maptoolkit/[email protected]/dist/maptoolkit.css" />
<style>
html, body { width: 100%; height: 100%; margin: 0; padding: 0; }
#map { width: 100%; height: 100%; }
</style>
</head>
<body>
<div id="map"></div>
<script>
const API_KEY = 'YOUR_API_KEY';
const map = new maptoolkit.Map({
container: 'map',
apiKey: API_KEY,
style: `https://styles.maptoolkit.net/maptoolkit/maptoolkit.summer.json?api_key=${API_KEY}`,
center: [-77.035, 38.875],
zoom: 12,
attributionControl: { compact: false }
});
map.addControl(new maptoolkit.NavigationControl(), 'top-right');
const geojson = {
type: 'FeatureCollection',
features: [{
type: 'Feature',
properties: {},
geometry: {
type: 'LineString',
coordinates: [
[-77.044211, 38.852924],
[-77.045659, 38.860158],
[-77.044232, 38.862326],
[-77.040879, 38.865454],
[-77.039936, 38.867698],
[-77.040338, 38.86943],
[-77.04264, 38.872528],
[-77.03696, 38.878424],
[-77.032309, 38.87937],
[-77.030056, 38.880945],
[-77.027645, 38.881779],
[-77.026946, 38.882645],
[-77.026942, 38.885502],
[-77.028054, 38.887449],
[-77.02806, 38.892088],
[-77.03364, 38.892108],
[-77.033643, 38.899926]
]
}
}]
};
map.on('load', () => {
map.addSource('line', {
type: 'geojson',
lineMetrics: true,
data: geojson
});
map.addLayer({
id: 'line',
type: 'line',
source: 'line',
paint: {
'line-color': 'red',
'line-width': 14,
'line-gradient': [
'interpolate', ['linear'], ['line-progress'],
0, 'blue',
0.1, 'royalblue',
0.3, 'cyan',
0.5, 'lime',
0.7, 'yellow',
1, 'red'
]
},
layout: {
'line-cap': 'round',
'line-join': 'round'
}
});
});
</script>
</body>
</html>Use the prompt below with any LLM to get the same result. Make sure the Maptoolkit MCP server is connected first — check out AI Integration & MCP to get started.
Use the Maptoolkit Connector. Create an interactive map with zoom level 12, centered around [-77.035, 38.875]. Draw a line along a route through Washington DC with a rainbow gradient color along its length.