Create a semicircle with Google Maps API v3. Coordinated and azimuth data are required. This is an adaptation of https://groups.google.com/forum/#!topic/google-maps-api/rKefiTZPXE8

drawSector.js

const drawSector = ({ lat, lng, r, azimuth, width, map }) => {
  const centerPoint = new google.maps.LatLng(lat, lng);
  const PRlat = (r / 3963) * (180 / Math.PI); // using 3963 miles as earth's radius
  const PRlng = PRlat / Math.cos(lat * (Math.PI / 180));

  let theta = 0;
  let gamma = (Math.PI / 180) * (azimuth + width / 2);
  let PGpoints = [];

  for (let a = 0; theta < gamma; a++) {
    theta = (Math.PI / 180) * (azimuth - width / 2 + a);
    let PGlat = lat + PRlat * Math.cos(theta);
    let PGlon = lng + PRlng * Math.sin(theta);

    PGpoints.push(new google.maps.LatLng(PGlat, PGlon));
  }

  PGpoints.push(centerPoint);

  const polygon = new google.maps.Polygon({
    path: PGpoints,
    strokeColor: "#4B0082",
    strokeOpacity: 1,
    map
  });

  return polygon;
};

// Example
/*
drawSector({
  lat: 49.994507,
  lng: 36.145742,
  r: 10,
  azimuth: 10,
  width: 45,
  map
});
*/