Arty uses gmaps plugin to show Google Maps. By default, the maps width is set to 100% and height is set to 0 and you can set the height of the map using 'gmap-xl/gmap-lg/gmap-md/gmap-sm/gmap-xs' classes.
<div id="map1" class="gmap gmap-xs" data-latitude="51.513569" data-longitude="-0.123443"></div>
<div id="map2" class="gmap gmap-sm" data-latitude="51.513569" data-longitude="-0.123443"></div>
<div id="map3" class="gmap gmap-md" data-latitude="51.513569" data-longitude="-0.123443"></div>
<div id="map4" class="gmap gmap-lg" data-latitude="51.513569" data-longitude="-0.123443"></div>
<div id="map5" class="gmap gmap-xl" data-latitude="51.513569" data-longitude="-0.123443"></div>