How to locate a latitude and longitude with jVector Map Plugin

Question

I know that google maps has markers to highlight certain points in the map. I am for some reason not comfortable putting this type of map on my site and love the jvector map effects. But I am not able to figure out how to define markers in the jVectorMap, does anybody have a clue as to how to define the markers in jVectorMap and highlight those points. I would also love to know how would you get to the certain point in jVector Map using latitude and longitude.

Thanks.

Answer 1

Now you can do that, new version of jVectorMap (0.2) introduces such feature with markers parameter. Check out demo here http://jvectormap.com/examples/markers-world/.

Answer 2

The jVectorMap world map uses the van der Grinten projection. The formula to convert from/to the map can be found this Wikipedia and Wolfram article.

You'll need to scale it to your map's size & offset, given the above formula projects the long/lat (-180 to 180 deg) to a (-1 to +1) cartesian grid.

Also, the angles in the formula should be in radians, not in degrees.

function vanDerGrinten(lat, lng) {
    lat = lat * Math.PI / 180;
    lng = lng * Math.PI / 180;
    var lng0 = 0;
    var A1 = 0.5 * Math.abs((Math.PI / (lng - lng0) - (lng - lng0) / Math.PI));
    var phi = Math.asin(Math.abs(2 * lat / Math.PI));
    var G = Math.cos(phi) / (Math.sin(phi) + Math.cos(phi) - 1);
    P = G * (2 / Math.sin(phi) - 1);
    Q = A1 * A1 + G;
    x0 = A1 * A1 * (G - P * P) * (G - P * P) - (P * P + A1 * A1) * (G * G - P * P);
    x1 = (A1 * (G - P * P) + Math.sqrt(x0));
    x2 = (P * P + A1 * A1);
    x = sgn(lng - lng0) * Math.PI * x1 / x2;
    y = sgn(lat) * Math.PI * Math.abs(P * Q - A1 * Math.sqrt((A1 * A1 + 1) * (P * P + A1 * A1) - Q * Q)) / (P * P + A1 * A1);
    return { _x: x, _y: y };
}