<%= stylesheet_link_tag 'https://cdn.jsdelivr.net/gh/openlayers/openlayers.github.io@master/en/v6.2.1/css/ol.css' %> <%= stylesheet_link_tag 'https://unpkg.com/ol-layerswitcher@3.5.0/src/ol-layerswitcher.css' %> <%= javascript_include_tag 'https://cdn.jsdelivr.net/gh/openlayers/openlayers.github.io@master/en/v6.2.1/build/ol.js' %> <%= javascript_include_tag 'https://unpkg.com/ol-layerswitcher@3.5.0' %> <%= javascript_include_tag 'map' %>