County Series Map Overlaps

The pre World War Two County Series maps (Epochs 1 to 4) were not produced from a national survey but from separate county surveys. As a consequence the map data for these Epochs overlay at county boundaries. In some cases there may be four maps (one each from four separate counties) in the same Epoch. Again, this is a characteristic of the data collection but it does present significant issues when trying to deliver these datasets as online mapping. Unlike contemporary Ordnance Survey map data offered through the Digimap Ordnance Survey Collection these maps cannot be presented as a seamless coverage for Great Britain. To do so would be problematic in terms of online map navigation and search.

A typical example of this overlap can be seen in the figure below:

The above figure shows the geographic extents of 1:10,560 County Series maps, 1st Revision 1888 to 1914 for a region of South-West England near the border of the counties of Worcestershire shown with a solid purple line, Gloucestershire shown with a solid green fill and Warwickshire shown with a hatched red fill. The county boundaries themselves are shown as a solid black line. In the Area of Interest highlighted we can see that the extents of County Series maps at this epoch for Gloucestershire and Warwickshire overlap. Looking at the same Area of Interest in Historic Digimap we see something like this:

In Historic Digimap we are presented with a double image when both the Gloucestershire and Warwickshire County Series maps are turned on. We can of course correct this by choosing to display maps from only one of the counties at this border region. Doing so, for example turning off display of Warwickshire results in Historic Digimap displaying a much cleaner map as can be seen below:

This County Series map overlap issue is complicated further because some of the maps will contain almost nothing but white space. Maps taken from the edge of a county may only have a little detail in one corner, the rest, where the neighbouring county is will be left blank. During use of Historic Digimap users may search for and find a legitimate map only to be confronted with a blank map. Consider the example shown below:

The map shown above shows the geographic extents of 2 County Series 1:10,560 map sheets for the same epoch mapped as part of Gloucestershire, shown as a red outline and Monmouthshire, shown as a blue outline. Clearly there is overlap between these sheets at the boundary between the 2 counties. Shown below are images of the two historic maps themselves:

Gloucestershire 1:10,560 County Series tile 13062NW1

Monmouthshire 1:10,560 County Series tile 50031001

On the first map from Gloucestershire topographic information has been captured for both the county of Gloucestershire itself, the small area bounded by the red line in the lower right hand corner plus a large region of Monmouthshire. On the other map captured as part of the survey of Monmouthshire topographic information is shown only for land which lies west of the Welsh border. Beyond the boundary into Gloucestershire topographic information is replaced by the large area of white space marked with the red hatched region.