To make this simpler, people first need to know a bit about what was possibly the first attempt at a European Common Market, known as  "The Hanseatic League", or Hansa, which began as a northern European trading confederation in the middle of the 13th century and continued for some 300 years. Its network of alliances grew to 170 cities and it protected its interests from interfering rulers and rival traders using a powerful fleet financed by its members, trading continued through the Baltic states, and intact still does today.

The most common pine used throughout the Georgian, Victorian and Edwardian periods was, contrary to today's common belief, Baltic Pine, often referred to as yellow pine, and in the UK was commonly known as Scots Pine.
As the periods changed from Georgian to Victorian to Eswardian, the widths that boards (floorboards, and roof sarking boards) were cut to generally became narrower. Exactly why is unsure. The Victorians uniformed the widths although there was never a set standard size. Edwardian boards were narrower again, but uniform widths also. 

Original Georgian boards are now very scarce and now command very high prices, in fact with the lack of UK demolition, and with the listing of buildings being introduced in 1947, which promotes the saving of, and protection of a lot of beautiful old buildings throughout the UK, all original floorboards are proving difficult to locate nowadays.

Despite most people today automatically jumping to "Pitch Pine" (just more assumptions), Baltic pine was actually the most commonly used pine in the Construction industry throughout the UK, with Scots Pine being widely used.

The Baltic Pines, as the name states,  originated from the Baltic states. Carried in the hull of the sailing ships of the time, as ballast, the timber was simply tipped out on the docksides and sold off for use in the building of those local towns and cities.