I am having issues with markers overlapping, please do not down vote as I am not highly schooled in javascript also I have looked at the different answers offered on stackoverfl
You can use the MarkerClusterer from google maps utility library.
Here is a step by step example: https://developers.google.com/maps/documentation/javascript/marker-clustering
And you can download the library from the google maps github repo: https://github.com/googlemaps/v3-utility-library/tree/master/markerclusterer