When using Google Maps in the HTML Composer, the following global jscript functions are available for gmaps:

function toggleLayer(mapId, layerName) – Toggle Layer Visibility

function toggleMarker(mapId, layerName, markerName) - Toggle Marker Visibility

function showAllMarkers(mapId)

function refreshLayer(mapId, layerName) //if layerName is null 
(or not specified) all layers will be refreshed

function panToAddress(address, mapId, zoom)

function panToPoint(lat, lng, mapId, zoom)

function drawBullseye(mapId, lat, lng, select, units, ringsNum,
 sizes, colors)