Thanks to this documentation link : https://www.typescriptlang.org/docs/handbook/triple-slash-directives.html
[Angular 6+] You only have to add this line at the beginning (meaning line 1, with nothing before) of your Typescript file :
/// <reference types="@types/googlemaps" />
[Angular 5-] You only have to add this line anywhere in your Typescript file imports :
import {} from "googlemaps";
Thanks to the answer below, you may also need to add a file <root>/index.d.ts
containing (didn’t need it though in my case) :
declare module 'googlemaps';