The County Series map system
The County Series map system was in use in the UK up to 1945, when the national series of maps based on the National Grid came into widespread use.
The County Series maps were produced at two scales - 1:10.560 and 1:2,500.
Each county was surveyed as a single unit and had an independent County Diagram on which was superimposed a grid system. A map was produced for each rectangle formed by the grid, each rectangle covering an area 6 miles by 4 miles.
The example below is the Renfrew County Diagram.
Each rectangle in the grid was identified by the County prefix and a roman numeral when it was published, for example, Renfrew XI. The published map scale was 6 inches to the mile, or 1:10,560. Depending on the size of the county, more or fewer rectangles of this size were produced.
Each large 6 inches to the mile map sheet could also be sub-divided into four quarters to be a more manageable size of paper sheet, although not every full sheet was sub-divided. These were known as the Quarter 6 inch maps. These quarter sheets were still at the original scale of 6 inches to the mile, and were named by using the full rectangle identifier with the addition of a suffix - NE, NW, SE or SW.
A further smaller map sheet at a larger scale was produced in many areas, with the full 6 inches to the mile map sheet being broken down into 16 smaller units at 25 inches to the mile, or 1:2,500.
The reference for the 1:2,500 map sheet coloured green in the diagram, above would be Renfrew XI 10.
Discontinuation of the County Series mapping system
As mentioned above, this system was in use up until 1945. The County Series system was replaced by the National Grid system as a result of the recommendations made by the Davidson Committee which met between 1935 and 1939. The replacement of the County Series was recommended because of disadvantages including:
Distortion at county edges making adjoining maps incompatible. Most counties at the 1/2500 scale surveys were carried out using a number of different map projections, each with their own central meridians. The result was that although the greater part of the country was mapped at 1:2500 scale, it did not form a national survey but rather a number of county surveys which did not fit together at their boundaries.
Largest scale was 1:2500 which was proving to be inadequate for recent legalization namely the Land Registration Act (1925) and the Town and Country Planning Acts (1925)
No house numbers were shown
No systematic revision for updating new developments - each map was updated every 10 to 20 years.
Due to each county having its own meridian there was no national referencing system.
The recommendations of the Davidson Committee included:
The recasting of 1:2500 scale (Twenty-five inches to one mile) map series on national instead of county lines using a national projection rather than separate county projections.
That a National Grid be superimposed on all large and small scale maps to provided one reference system for the whole country.
That the International metre be adopted as the unit on which the system be based (this was a very far-sighted recommendation at that time, as metrification did not become widespread in the UK until the 1970s).
That there would be a system of continuous revision for large scale maps.
That the 1:1250 or 50" to 1 mile scale to be adopted for urban areas.
That house numbers would be shown.
The result was the development of the National Grid system.