Simple Map

HTML

<div id="map"></div>
<!-- Replace the value of the key parameter with your own API key. -->
<script src="https://maps.googleapis.com/maps/api/js?key=AIzaSyCkUOdZ5y7hMm0yrcCQoCvLwzdM6M8s5qk&callback=initMap" async defer></script>

CSS

/* Always set the map height explicitly to define the size of the div
 * element that contains the map. */
#map {
  height: 100%;
}
/* Optional: Makes the sample page fill the window. */
html, body {
  height: 100%;
  margin: 0;
  padding: 0;
}

JavaScript

var map;
const center = {lat: 41.536558, lng: -8.627487};
const radius = 25;

function initMap() {
  map = new google.maps.Map(document.getElementById('map'), {
    center,
    zoom: 8
  });
  
  var antennasCircle = new google.maps.Circle({
      strokeColor: "#FF0000",
      strokeOpacity: 0.8,
      strokeWeight: 2,
      fillColor: "#FF0000",
      fillOpacity: 0.35,
      map: map,
      center,
      radius
    });
  map.fitBounds(antennasCircle.getBounds());

	map.addListener('click', function(e) {
    isInCircle(e.latLng, false);
  });
  
  antennasCircle.addListener('click', function(e) {
    isInCircle(e.latLng, true);
  });
}
function degreesToRadians(degrees) {
  return degrees * Math.PI / 180;
}

function distanceInMBetweenEarthCoordinates(lat1, lon1, lat2, lon2) {
  var earthRadiusM = 6371000;

  var dLat = degreesToRadians(lat2-lat1);
  var dLon = degreesToRadians(lon2-lon1);

  lat1 = degreesToRadians(lat1);
  lat2 = degreesToRadians(lat2);

  var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
          Math.sin(dLon/2) * Math.sin(dLon/2) * Math.cos(lat1) * Math.cos(lat2); 
  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
  return earthRadiusM * c;
}


function isInCircle(latLng, isInside) {
  const distance = distanceInMBetweenEarthCoordinates(latLng.lat(), latLng.lng(), center.lat, center.lng);

  const calculationResult = distance <= radius;
  console.log(calculationResult, isInside)
  alert("Calculation result is inside: " + calculationResult + " circle was clicked: " + isInside);
}