Hierarchical or Significant digit Code

I need explanation on limited factor

Hierarchical (significant digits) codes work through from general qualities to more and more specific qualities as you go trough the code.

So, to code for a city, the first digit could be continent:

1 – Europe
2 – Asia
3 – Africa
4 – America

etc.

The second code could be the country

1 – UK
2 – France
3 – Germany

etc

The third could be the city

1 – Berlin
2 – Munich
3 – Frankfurt

Do a code of 133 means Errope, Germany, Munich.

It can be helpful to code like this because the code has a structure that can be useful. So, if you want a list of all cities in Africa, just look for any code number starting with 3.

All cities in France will start with 12.

If all the worlds cities were just listed alphabetically and assigned a sequence code, the processing that could be csrried out would be less convenient.