Getting polygon boundaries of City in JSON from Google Maps API?

No, there is no way to steal Google's data. May be you could look at OpenStreetMap which is designed for people to download.

You can get polygon coordenates in json for using with googlemaps using openstreetmap. Go to http://nominatim.openstreetmap.org/ search a place like "Partido de Ituzaingó"

click on "details"

Look for OSM ID and copy it (control+c), example: 2018776

paste the ID in http://polygons.openstreetmap.fr/index.py and download the polygon

As an alternative to Google Maps API, OpenStreetMap may help you to search for a city by name in this page http://nominatim.openstreetmap.org/ . Then review search results, and you can get region coordinate in GeoJSON format e.g (http://nominatim.openstreetmap.org/details.php?place_id=145126778) to get mashhad geojson coordinates in Administrative tab

I've found a work around solution for this problem.

1. Go to www.gadm.org/country
2. Choose your country and select Google Earth .kmz file format
3. Choose the level you need (level 3 is the deepest with all small towns/cities)
4. Download the file (can be large)
5. Unzip the .kmz file (You'll find a .kml which is XML)
6. Open it with Sublime or notepad++ (the file will probably be too large for other text editor)
7. Search by city name and copy data below (Search can take 1 to 4 seconds with large file)

You can use lat,long data and parse it into an array. This solution is working well, but the quality of the path is sometimes rough.

To get polygon boundaries just add format=json to your request!

So instead of https://nominatim.openstreetmap.org/search.php?q=Warsaw+Poland&polygon_geojson=1

use

https://nominatim.openstreetmap.org/search.php?q=Warsaw+Poland&polygon_geojson=1&format=json

By adding &format=geojson you can get a valid geojson response