Custom Settings revisited !!!

I remember nostalgically the first major technical document I penned. It was for a product/project I had worked on - and the comments of the reviewer were Ispita why do you use such flowery language ~ I guess the person was being generous~ what was implied was ~ Ispita keep it short and simple.
Such comments are always priceless - and act as sharpening stones.
Apart from the two S mentioned above I now add a third dimension - spicy. So anything I write essentially has the three S- Simple, Short , Spicy ( na na don't run your horses of imagination - spice essentially  means -  the action on peppering your textual creation with anecdotes and personal touch , don't you look for yellow journalism - u will get none).

That reminds me this is not about - "How to write in Queen's language?" this blog will talk briefly about  "Custom Settings" and in particular about those which fall in the category of List custom settings.

So what are Custom Settings?

Custom settings are just like custom objects which act as placeholders to hold information which may tied to:-
1) an organization
2) a profile
3) a specific user

This leads us to the obvious question if its similar to custom objects then why create another data structure with similar traits? What purpose does it serve?
In pure technical terms you can say - "All custom settings data is exposed in the application cache, which enables efficient access without the cost of repeated queries to the database."  In layman's language lesser use of select statements and faster code execution.
Also they act as custom application wide global variables ( These are the List custom settings).
Now coming to the type of Custom settings . There are two types of custom settings:
List Custom Settings
This is the set of data which is available to the whole organization and remains the same irrespective of the profile or user accessing it. Its the socialistic type of custom setting same for everyone across the organization.Also since its cached and does not require issuing of costly SOQL queries they don't add to your overall tally of SOQL queries issued and thus help you in not breaching the governor limits.
Hierarchy Custom Settings
But what if you need a set of data which should morph or return different info based on which category of people is accessing it or which user is accessing it? So now the custom setting is not socialistic and return information based upon the rights of the user accessing it- or information is returned keeping in view the hierarchy- those are called the "Hierarchy Custom setting".
Click on the picture below for enlarged view.

Now how to access this via code in apex.
General syntax :-

Map<string , CustomSettingName > Variable Name = CustomSettingName.getAll();   

Here w.r.t. above diagram the syntax will be:-

Map<string , AppSetting> CST = AppSetting.getAll();   
string  strURL1 = CST .get('URL').compartment1__c;    

string  strURL2 = CST .get('URL').compartment2__c;    

So strURL1 contains àhttp://login.salesforce.com   and  strURL2 contains àhttp://test.salesforce.com  

I know you will say custom settings are so easy - but believe me whenever I start using them I always tend to forget some of the steps and go about re-inventing the wheel - so this time I thought of writing the steps for future reference.