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Line gradient

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Create a gradient line using an expression

Use the line-gradient paint property and an expression to visualize distance from the starting point of a line.

This source code of this example is adapted from the MapLibre GL JS example - Create a gradient line using an expression.

Uncomment the following line to install leafmap if needed.

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# %pip install "leafmap[maplibre]"

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import leafmap.maplibregl as leafmap

To run this notebook, you will need an API key from MapTiler. Once you have the API key, you can uncomment the following code block and replace YOUR_API_KEY with your actual API key. Then, run the code block code to set the API key as an environment variable.

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# import os
# os.environ["MAPTILER_KEY"] = "YOUR_API_KEY"

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m = leafmap.Map(center=[-77.035, 38.875], zoom=12, style="streets")

geojson = {
    "type": "FeatureCollection",
    "features": [
        {
            "type": "Feature",
            "properties": {},
            "geometry": {
                "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],
                ],
                "type": "LineString",
            },
        }
    ],
}
source = {"type": "geojson", "lineMetrics": True, "data": geojson}
m.add_source("line", source)

layer = {
    "type": "line",
    "source": "line",
    "id": "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"},
}
m.add_layer(layer)
m