How to create a google map block to display number of nodes for a content type
Use Geofield_map module:


  Geofield Map is an advanced, complete and easy-to-use Geo Mapping
  solution for Drupal 8, based on and fully compatible with the Geofield
  module, that lets you manage the Geofield with an interactive Map both
  in back-end and in the front-end.
  
  It represents the perfect solution to:
  
  geolocate (with one or more Locations / Geofields) any fieldable
  Drupal entity throughout an Interactive Geofield Map widget; render
  each Content's Locations throughout a fully customizable Interactive
  Geofield Map Formatter; expose and query Contents throughout fully
  customizable Map Views Integration; implement advanced front-end
  Google Maps with Marker Icon &amp; Infowindow advanced customizations,
  custom Google Map Styles and Marker Clustering capabilities; customize
  Map Geometries properties (Lines &amp; Polylines, Polygons, Multipolygons,
  etc.), based on Google Maps Polygons APIs;


Take a look at Demo.

So, in summary, you need to install this module and add it to your content type.
then with creating a custom view, you can achieve what you want.