context.beginPath();
for (var i = 0; i < (length of elevations); i++){
    context.moveTo(i*canvas.width/(length of elevations), canvas.height-elevations[i]);
}
context.moveTo(canvas.width+1, canvas.height+1);
context.moveTo(-1, canvas.height+1);
context.closePath();
context.fillStyle = "#F00";
context.fill();
alert("attempting to fill");