Edit in JSFiddle

var points = [ {x:120,y:110}, {x:150,y:190}, {x:280,y:150}];

var renderMarker = function(point) {
    ctx.save();
    ctx.translate(point.x, point.y);
    ctx.rotate(Math.PI/4);
    ctx.fillRect(-5,-5,10,10);
    ctx.restore();
};

var renderScannerRing = function(point, radius) {
    ctx.save();
    ctx.translate(point.x, point.y);
    ctx.beginPath();
    ctx.arc(0,0,radius,0,2*Math.PI);
    ctx.stroke();
    ctx.restore();
};

var ctx = document.getElementById('map').getContext('2d');
ctx.fillStyle = ctx.strokeStyle = "rgba(120,256,120,1.0)";
ctx.lineWidth = 5;

var i;
for(i=0; i<points.length; i++) {
    renderMarker(points[i]);
    renderScannerRing(points[i], 75);
}

<canvas id="map" width="400" height="300"></canvas>

#map {
    background: url(http://droneage.com/img/battle/bg/starfield-navy.jpg)
}