Для карты используются значения по умолчанию:
container_id: "map_container",
id: "map",
type: "ROADMAP", // HYBRID, ROADMAP, SATELLITE, TERRAIN
center_latitude : 0,
center_longitude: 0,
disableDefaultUI: false,
disableDoubleClickZoom: false,
draggable: true,
mapTypeControl: null, // display the map type dropdown, unless set to false it will be displayed
detect_location: false, // should the browser attempt to use geolocation detection features of HTML5?
center_on_user: false, // centers map on the location detected through the browser
zoom : 1, // initial zoom
maxZoom: null, //max zoom level
minZoom: null, //min zoom level
auto_adjust: true, //adjust the map to the markers if set to true
auto_zoom: true //comes with auto_adjust. Choose whether or not you want to use an automatic zoom or the one you set in the 'zoom' option.
bounds: [] //adjust map to these limits. Should be [{"lat": , "lng": }, {"lat": , "lng": } ...]
Я не уверен, как переопределить настройки по умолчанию для всего приложения, но вы можете перейти с ROADMAP на TERRAIN в представлениях:
<%= gmaps({"map_options" => { type => "TERRAIN" })%>