If you see the error message “MissingKeyMapError” in your browser console when using Google Maps this is due to recent change in the Google Maps terms of service requiring that you create an API key and include it on pages on your site that use Google Maps.
You can find a quick guide to generating an API key and including it with your store locator here.
For more information about why you need an API key and Google Maps licensing in general check out this post.