How to take a screenshot of a something bigger than the screen?

To get bigger images from Google Maps, you need to use Google Map Saver.

Google Map Saver (GMS) offers you an easy and free way to download big Google Maps on your PC as JPEG, PNG-8, PNG-24, BMP or Targa files. GMS is light (only ~400 KBytes) and very easy to run since doesn’t have an installer. You can save maps up to 12000 x 12000 pixels!

If you are using Firefox, the FireShot extension should do the job - it can capture just what's visible OR the entire page depending on what you want.

Any Website, Any Size.

Use a combination of Firefox, Developer tools, Responsive Design Mode, and Screenshot, all available without extra software or add-ons:

Tested on Firefox 52.x, probably works in earlier versions.

You can of course also leverage add-ons as outlined in this superuser answer.

Works on any website which would normally limit the viewing area to your window size, as shown on this very large Sky picture:

Image source: https://www.google.com/sky/ (i.e. not Google Map) at 5401×3603 pixels and 8.9 MB