Function that takes latitude/longitude of a single point and returns x/y position as plotted on an equirectangular map.

lltoXY.js

// Function
function lltoXY(options) {
	var x = (options.lon + 180) * (options.width / 360);
	var y = ((options.lat * -1) + 90) * (options.height / 180);
	return { x: x, y: y };
}

// Usage
var position = lltoXY({
	lat: 25.26,
	lon: 55.3,
	width: 300,
	height: 200
});