Thanks to you all! The Flip book on the OS is really wonderful and will order Map of Nation. Haven't found what I needed yet, but great resources.
My family worked for generations for the OS and have found them in Scotland and England from the mid 1840s onward but they are from Ireland and, although I have no proof, I believe that they might have taken up with the mapping of Ireland in the 1830/1840 period. I have their county of origin and not much else so I'm trying to link them to the path of the mapping project by town where I can then search for their parish records as well as try to back up my theory about where they first joined on. I find it a fascinating path they took..however it is maddening as an amateur genealogist to trace a family that hopped around as much as they did in that line of work.
Again, many thanks!