Tutorial - Markers

Create a map with a tile layer, define some data, and create a feature layer.

Step 1

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Create a marker feature and set the data. The default marker feature looks just line a point feature -- circles with borders.

Step 2

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Markers have many different symbols and style options:

symbol: the symbol shape, enumerated in geo.markerFeature.symbols. This includes ellipse, triangle (isosceles triangles), rectangle, oval, and drop. There are symmetric repeating patterns such as cross4, flower6, star5, jack6, and drop8, where the number is the rotational symmetry from 2 to 16.
symbolValue: a number that modifies how the symbol appears, usually in the range of [0, 1]. This is often the ratio of the minor axis of the symbol to its major axis. For triangle, it is the length of the base side compared to the identical sides.
rotation: the rotation in radians.
rotateWithMap: a boolean; if true, the symbol rotates when the map is rotated. If false, it remains in the same orientation on the screen.
radius: in pixels. Depending on strokeOffset and radiusIncludesStroke, this can include half or all of the stroke width.
radiusIncludesStroke: if truthy or undefined, the radius includes the strokeWidth based on the strokeOffset. If defined and falsy, the radius does not include the strokeWidth; set this to false if scaleWithZoom is set to "fill".
strokeWidth: the width of the stroke around the symbol in pixels.
strokeOffset: the position of the stroke compared to the radius. This can only be -1 (inside), 0 (centered at the radius), or 1 (outside).
scaleWithZoom: one of the values defined in geo.markerFeature.scaleModes. If none, the symbols remains the same size when the map is zoomed. This can also be fill, stroke, or all, in which case the symbol will change size when the map is zoomed. If scaling with zoom, the radius and strokeWidth are in pixels at zoom level 0.
fillColor
fillOpacity
strokeColor
strokeOpacity:

Step 3

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When scaling a marker with the map, the radius and stroke width are the values at zoom level 0.

Step 4

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Markers are drawn efficiently, even if they all have different styles. This creates a large sample of symbols, each with a different style.

let count = 1000, markers = [];

for (let i = 0; i < count; i += 1) {
  let symbol = Math.floor(Math.random() * geo.markerFeature.symbols.length);
  let symbolValue = Math.random();
  if (symbol === geo.markerFeature.symbols.triangle) {
    // triangles use a larger range than most symbols
    symbolValue *= 2;
  } else if (symbol >= geo.markerFeature.symbols.arrow && symbol < geo.markerFeature.symbols.arrow + geo.markerFeature.symbols.arrowMax) {
    // arrow symbols can take an array to specify their shape
    symbolValue = [
      Math.random(),
      Math.random(),
      Math.random() > 0.1 ? Math.random() : 0,
      Math.random() >= 0.5
    ];
    if (symbol >= geo.markerFeature.symbols.arrowBase) {
      symbolValue[0] /= 2;
      symbolValue[1] /= 2;
      symbolValue[2] /= 2;
    }
  }
  markers.push({
    x: Math.random() * 50 - 120,
    y: Math.random() * 40 + 10,
    radius: Math.random() * 30 + 5,
    strokeWidth: Math.random() > 0.1 ? Math.random() * 5 : 0,
    symbol: symbol,
    symbolValue: symbolValue,
    fillColor: {r: Math.random(), g: Math.random(), b: Math.random()},
    fillOpacity: Math.random(),
    strokeColor: {r: Math.random(), g: Math.random(), b: Math.random()},
    strokeOpacity: 0.5 + Math.random() * 0.5,
    rotation: Math.random() * Math.PI * 2
  });
}
feature.data(markers).position(d => d).style({
  radius: d => d.radius,
  strokeWidth: d => d.strokeWidth,
  symbol: d => d.symbol,
  symbolValue: d => d.symbolValue,
  fillColor: d => d.fillColor,
  fillOpacity: d => d.fillOpacity,
  strokeColor: d => d.strokeColor,
  strokeOpacity: d => d.strokeOpacity,
  rotation: d => d.rotation,
  scaleWithZoom: geo.markerFeature.scaleMode.none,
  rotateWithMap: true
}).draw();

Step 5

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