Develop Reference

Create a square / polygon with a size in meters in Google Maps in JS

I'm going crazy soon! I've read pretty much all of the Google Maps JavaScript API V3 documentation but I can't find a way to develop the following use case:
I want to create a square / circle / polygon with a specific size in meters. The radius of the circle, or the distance between LAT and LNG in meters.
I know it's possible to measure the distance in meters between to LatLngs, but I want to create it wit that dimension.
Is there anybody who know's how to do this? That would be amazing!

You can use the Geometry library and more specifically the computeOffset method.
The distance parameter is in meters, although this is not clear from the docs.
Here is a simple example using the Rectangle class but you can use any shape. For circles, you don't need this as the radius is already expressed in meters.
For Rectangles, you need to calculate the bounds (ne for north-east and sw for south-west). Here I create a rectangle (a square in this case) with a 500 meters diagonal.
For Polygons, you need to provide a path instead of bounds, but the method remains the same. If you know the starting point, the distance and the heading between every path point, you can come up with any kind of shape.
You need to load the Geometry library in the API call:
https://maps.googleapis.com/maps/api/js?libraries=geometry
function initialize() {
var sw = new google.maps.LatLng(52.51,13.41);
var mapOptions = {
zoom: 13,
center: sw,
mapTypeId: google.maps.MapTypeId.ROADMAP
};
var map = new google.maps.Map(document.getElementById("map-canvas"), mapOptions);
var marker = new google.maps.Marker({
position: sw,
map: map,
label: 'SW'
});
var ne = google.maps.geometry.spherical.computeOffset(sw, 500, 45);
var marker = new google.maps.Marker({
position: ne,
map: map,
label: 'NE'
});
var rectangle = new google.maps.Rectangle({
strokeOpacity: 0,
strokeWeight: 0,
fillColor: '#FF0000',
fillOpacity: .6,
bounds: new google.maps.LatLngBounds(sw,ne),
map: map,
zIndex: 0
});
}
initialize();
#map-canvas {
height: 150px;
}
<div id="map-canvas"></div>
<script src="https://maps.googleapis.com/maps/api/js?libraries=geometry&key=AIzaSyCkUOdZ5y7hMm0yrcCQoCvLwzdM6M8s5qk"></script>

Drawing a POLYGON from initial position

My problem is: I need to draw with mode POLYGON with a initial point, like a marker or another element. For example - JSFiddle Example
With marker:
var initialPosition = new google.maps.Marker({
position: {
lat: -22.397542,
lng: -46.884630
}
});
This position is given without any user interaction. How can I do that?
In my example, how can I draw a polygon starting from marker without click it, making marker position my first polygon point?

You could do the following: use addListenerOnce to detect a click on the map (only once). This will allow to create a Polygon that goes from your marker position, to where the user clicked, and back to the marker position.
By setting the editable property to true, you can then move each Polygon point separately, and add segments by dragging the existing segment(s) middle point(s).
Here is a working example:
function initialize() {
var myLatLng = new google.maps.LatLng(46.2, 6.17);
var mapOptions = {
zoom: 4,
center: myLatLng,
mapTypeId: google.maps.MapTypeId.ROADMAP
};
var map = new google.maps.Map(document.getElementById("map-canvas"), mapOptions);
var marker = new google.maps.Marker({
position: myLatLng,
map: map
});
google.maps.event.addListenerOnce(map, 'click', function(e) {
var origin = marker.getPosition();
var coords = [
origin,
e.latLng,
origin,
];
var poly = new google.maps.Polygon({
map: map,
paths: coords,
editable: true,
strokeColor: '#FF0000',
strokeOpacity: 0.8,
strokeWeight: 2,
fillColor: '#FF0000',
fillOpacity: 0.35
});
});
}
initialize();
#map-canvas {
height: 150px;
}
<div id="map-canvas"></div>
<script src="https://maps.googleapis.com/maps/api/js"></script>

How do I set a marker's size by a number of purchases?

In an e-commerce system I'm building, I want to use google maps api to show the origins of the purchases. I want the markers to be shaped as a circle, and I want that circle's size to be determined by the number of purchases made from that particular city. Let's say there were 100 orders from NYC and 200 from Boston, The Boston's circle will be twice the size.
How can I do that?

Your marker icon can be a symbol (SVG path) so you can scale it to your convenience.
The following example upscales the symbol each time you add one to the map. You can easily reuse that to your use case.
var map;
var polyLine;
var polyOptions;
var iconSize = 0.5;
function initialize() {
var mapOptions = {
zoom: 5,
mapTypeId: google.maps.MapTypeId.ROADMAP,
center: new google.maps.LatLng(0,0)
};
map = new google.maps.Map(document.getElementById('map-canvas'), mapOptions);
google.maps.event.addListener(map, 'click', function(event) {
addPoint(event);
});
}
function addPoint(event) {
var icon = {
path: "M-20,0a20,20 0 1,0 40,0a20,20 0 1,0 -40,0",
fillColor: '#FF0000',
fillOpacity: .6,
anchor: new google.maps.Point(0,0),
strokeWeight: 0,
scale: iconSize
}
var marker = new google.maps.Marker({
position: event.latLng,
map: map,
draggable: false,
icon: icon,
zIndex : -20
});
map.panTo(event.latLng);
iconSize += .1;
}
initialize();
JSFiddle demo

How To Get Coordinates of the google maps Corners?

I need to draw polygon with just four coordinates that is for the four corners of the loaded map in zoom 13 on other hand get coordinates of the whole map to show to user. ( user search the specific area with draw a polygon on the map but if he/she don't draw a polygon i want to draw a polygon in size of the projected map for him/her and show the result. )

Create the map at zoom: 13
var map = new google.maps.Map(document.getElementById("map"), {
center: {lat: 51.561162, lng: -0.163331},
zoom: 13
});
Then use map.getBounds() to get the LatLngBounds of the visible map.
var bounds = map.getBounds();
You can then use this to get the LatLng coordinates of the South West and North East corners:
var NECorner = bounds.getNorthEast();
var SWCorner = bounds.getSouthWest();
Then you can use those to work out the coordinates for the other two corners:
var NWCorner = new google.maps.LatLng(NECorner.lat(), SWCorner.lng());
var SECorner = new google.maps.LatLng(SWCorner.lat(), NECorner.lng());
And finally draw the polygon, using those corners for the paths array:
var polygon = new google.maps.Polygon({
map: map,
paths: [NWCorner, NECorner, SECorner, SWCorner],
fillColor: 'red',
fillOpacity: 0.7
});

Thanks duncan
Lemme write it in short form for Kotlin developers
var bounds = googleMap!!.projection.visibleRegion.latLngBounds
var neCorner = bounds.northeast
var swCorner = bounds.southwest
var nwCorner = LatLng(neCorner.latitude, swCorner.longitude)
var seCorner = LatLng(swCorner.latitude, neCorner.longitude)

Google maps - add road directions, circle, postal code areas

I got a basic map running using google maps v3
Next features that I would like to add include:
draw line as road directions instead of direct point to point polyline
draw a circle 75 km circle around from a specific point
highlight the postal code of a specific point.
I Would appreciate people's thoughts on these topics
var geocoder;
var map;
function fnPresentMap()
{
geocoder = new google.maps.Geocoder();
var locationArray = new Array();
locationArray[0] = new Array();
locationArray[1] = new Array();
locationArray[0][0] = document.getElementById('LAT_OUT_1').innerHTML;
locationArray[0][1] = document.getElementById('LON_OUT_1').innerHTML;
locationArray[1][0] = document.getElementById('LAT_OUT_2').innerHTML;
locationArray[1][1] = document.getElementById('LON_OUT_2').innerHTML;
var latlng = new google.maps.LatLng(44, -75);
var myOptions = {
zoom: 8,
center: latlng,
mapTypeControl: true,
mapTypeControlOptions: {
style: google.maps.MapTypeControlStyle.DROPDOWN_MENU},
navigationControl: true,
mapTypeId: google.maps.MapTypeId.ROADMAP
};
map = new google.maps.Map(document.getElementById("map"), myOptions);
var myLatlng;
var image_name;
for (var count = 0; count < locationArray.length; ++count){
image_name = "img/marker_"+(count+1)+".png";
myLatlng = new google.maps.LatLng(locationArray[count][0],locationArray[count][1]);
var marker = new google.maps.Marker({
position: myLatlng,
map: map,
icon: image_name
});
}
// re-center
var centerLocation = new google.maps.LatLng(locationArray[0][0],locationArray[0][1]);
map.setCenter(centerLocation);
// show line
var points = [
new google.maps.LatLng(locationArray[0][0],locationArray[0][1]),
new google.maps.LatLng(locationArray[1][0],locationArray[1][1])
];
var line = new google.maps.Polyline({
map: map,
path: points,
strokeColor: "#FF0000",
strokeWeight: 2,
strokeOpacity: 1.0
});
}

To render road directions between two specific points, you need to use the Google Maps API directions service. If you check out the documentation you will find pretty straightforward examples to make a directions request and render the results on a map as a line between the two points.
I think the best approach for drawing a circle around a point is to draw a polygon with enough points to approximate a circle. You can find a good example of this here.
To highlight the postcode at a specific point, I suggest you use the Google Maps API reverse geocoding service (convert from a latitude/longitude to a human readable address). You can extract the postcode from the JSON response you get back and then display it on the map using a infoWindow or some other kind of overlay.