Since its official foundation in 1792 the OS started to work on producing maps, initially for the military at 1″ to a mile then later a wide range of large and small scales for various uses.
They realised that the development of surveying for making accurate maps that would be consistent across the whole of the UK requires not only the relative position (trig points) of the features but also their elevation (level/datum).
I have focused my research on the levelling aspect of the operation as there are very many more points of level or datums (bench marks used for heights) around than there are for triangulation pillars (used for relative position).
So to reproduce to scale an accurate representation of the features on the ground you need to collect a vast amount of data points.
I like the levelling aspect as I can understand how it works and how it can be applied to everyday use in a practical way, using basic and simple but accurate, instruments. I am still overwhelmed by the sheer scale of the work needed to collect the information, put it into some order and apply it to make the best maps in the world (at that time and even now).
Nowadays of course things have evolved using the all seeing, all knowing computer that collects millions of pieces of data in the blink of an eye and converts this into very accurate maps.
The Ordnance Survey still has its work cut out to make sense of everything collected to produce digital mapping that is so essential in modern day living. Take the GPS as an example!
Why do I still hang onto the original concepts? One day I say we may need to revert to pre battery/electronic era but its nice to be able to say I/we can still do it anyway, it would take longer and may not be so accurate but it will still work!