You can add a longitude/latitude (lon-lat) grid to a LuciadRIA application by creating a GridLayer and passing a LonLatGrid instance to it.

Such a grid layer gives users a point of reference when they’re panning and moving the map.

Program: Creating a grid layer with a lon-lat grid
function createGridLayer() {
  var lonLatGrid = new LonLatGrid();
  return new GridLayer(lonLatGrid);
}

After creating the layer, you add the layer to the map.

Program: Adding the grid layer to the map
map.layerTree.addChild(createGridLayer(), "top");