Data for Cupertino comes preloaded. To view gym locations in other nearby areas, click around the map. Click on the gyms/eggs/bosses to view more info about ongoing raids.
The beta website for CupertinoPokemap contains a variety of small changes, including better "Get Directions" links, switching to OpenStreetMap tiles from Google Maps, and only loading in necessary gym data to save on data and bandwidth.
Please note that this map is still in the public beta testing phase, it may go offline or become unavailable at any time.