Assuming the urls are saved to a database where they each have id and the URL saved.
For example a URL
www.example.com (let's say with id 1000) would possibly be shortened to
Is the URL
id=1000 shortened to
c1hd5 with base64 or similar or are the ids shortened?
The 566 id could be shortened like this: 1 = 1, 2 = 2, ... 9 = 9, 10 = a. The 1000 id would be fE if we used every possible letter from a-Z and - _.
Is it good idea to use ids from database to shorten urls?