Also when you are starting with a new number, do all the landmarks need to be unique, or can you re-use the same building but with a different number of windows etc. Or are the items all the same, just in a different order?
It could be anything, what you said would work beautifully if it has occurred spontaneously to you. The key thing is it has to be very very natural to you but may not make any sense at all to others.
Example, one of the building I have assigned the number 78 as it is an old building and my father's age is around that.
> do all the landmarks need to be unique
Again it is a very personal decision. For me currently it is one pair of number per landmark as I did not want to 'overload' my system. But if I think about it now, maybe after sometime when I'm comfortable with my current system I can assign another number to the same landmark... But I'm not going to risk it now :-).
If you really want to try it out, start with one thing now and see how it goes before doing for others.
Btw, I discovered this when reading 'Moonwalking with Einstein' (referenced by another commentator here). This book was in reading list of Bill Gates couple of years back.
To illustrate my earlier point, the title of the book does not make any sense at all, but that series of words is used by somebody in the book to remember certain things.
The field of memory training has a system (called the major system) for converting arbitrary numbers into words by assigning distinct sounds to the 9 digits - 0 is s, 1 is t(d), 2 is n and so on.
For example, 95 would be p + l sound - say a pillow. Try to visualize a giant pillow (have something exaggerated and preferably silly) on that spot.