Polyline Layer

You can add lines to maps to display paths/ways made out of points to users using PolylineLayer().

FlutterMap(
    options: MapOptions(),
    children: [
        PolylineLayer(
            polylineCulling: false,
            polylines: [
                Polyline(
                  points: [LatLng(30, 40), LatLng(20, 50), LatLng(25, 45),],
                  color: Colors.blue,
                ),
            ],
        ),
    ],
),

Due to the nature of the Earth being a sphere, drawing lines perfectly requires large amounts of difficult maths that may not behave correctly when given certain edge-cases.

Avoid creating large polylines, or polylines that cross the edges of the map, as this may create undesired results.

Excessive use of polylines or use of complex polylines will create performance issues and lag/'jank' as the user interacts with the map. See for more information.

You can try the below methods to try to reduce the lag:

• Keep saveLayers set to false (which is default). This will reduce rendering times, however it will also reduce the visual quality of the line at intersections.

• Enable polylineCulling. This will prevent the calculation and rendering of lines outside of the current viewport, however this may not work as expected in all situations.

• Simplify the polyline by reducing the number of points within it. This will reduce calculation times, however it will make the line less precise. This is recommended, for example, when zoomed further out. You may be able to use an external Flutter library for this, called 'simplify'.

Polylines (polylines)

As you can see PolylineLayerOptions() accepts list of Polylines. Each determines the shape of a polyline by defining the LatLng of each point. 'flutter_map' will then draw a line between each coordinate.

Property	Type	Defaults	Description
points	List<LatLng>	required	The coordinates of each point
strokeWidth	double	1.0	Width of the line
color	Color	Color(0xFF00FF00)	Fill color
borderStrokeWidth	double	0.0	Width of the border of the line
borderColor	Color	Color(0xFFFFFF00)	Color of the border of the line
gradientColors	List<Color>?		List of colors to make gradient fill instead of a solid fill
colorsStop	List<double>?		List doubles representing the percentage of where to START each gradient color along the line
isDotted	bool	false	Whether to make the line dotted/dashed instead of solid

Converting Formats

You may have a polyline with 'Google Polyline Encoding' (which is a lossy compression algorithm to convert coordinates into a string and back). These are often returned from routing engines, for example. In this case, you'll need to decode the polyline to the correct format first, before you can use it in a Polyline's points argument.

One way to accomplish this is to use another Flutter library called 'google_polyline_algorithm', together with a custom method. You can use the code snippet below, which can just be pasted into a file and imported whenever needed:

import 'package:latlong2/latlong.dart';
export 'package:google_polyline_algorithm/google_polyline_algorithm.dart'
    show decodePolyline;

extension PolylineExt on List<List<num>> {
  List<LatLng> unpackPolyline() =>
      map((p) => LatLng(p[0].toDouble(), p[1].toDouble())).toList();
}

You can then use the package and the above snippet by doing:

import '<code_snippet_path>'

decodePolyline('<encoded-polyline>').unpackPolyline(); // Returns `List<LatLng>` for a map polyline