Creating a base map for a Town & City Historical Map®

By Giles Darkes — HTT Cartographer

Most of the maps that we produce use a digitised version of an OS map from somewhere between 1880 and 1930 as the base map, and we then add the historical information to it. The OS map is converted into a vector digitised form, and that means capturing the main features on the map and converting them into points, lines and areas.  Once they’ve been converted, it means that we can apply a cartographic style to them, and then add the historical information.

We’re currently working on maps of St Andrews, Brecon and Hay-on-Wye.  Using part of the map of St Andrews as an example, the OS map looks like this:

The basic digitised file is produced for us by commercial cartographers and digitisers, Lovell Johns. Not all features are captured (no text, for example) and minor features such as postboxes, trees, and spot heights are omitted. When supplied to us, the mapped features have no labels, or attributes attached to them, and the colours used are arbitrary.  The basic digitised data has then to be processed to add the styles we use for our different map series, and we need to make sense of the base map before adding information gathered by the local team.

Some of the basic information is evident on the OS map: churches, public buildings like banks and halls are labelled using the OS information as the source. That information needs to be added to the map.

Items like the hachuring (which denotes a slope) have to be created and applied to the base map.  In its basic digitised state, you can see that the hachures within United College’s grounds appear as a polygon in the basic file, but we need to convert that polygon to a symbol for hachures:

We have also applied the right colours to the buildings, using the OS map for information, plus reasoning and checking other sources if they are easily available: yellow for the post-medieval church, gold for a surviving medieval building, and a colour for university buildings. The other buildings of lesser importance are given a grey fill, and the gardens of large houses and ‘public’ buildings are given a green fill.

At this stage, we don’t have any specific or detailed information about the historical information to be added, so we don’t know the full extent of the surviving medieval building of St Saviour — it could be that the part of the building to the north of the gold part here is also medieval, but we’ll be given that information by the team of local historians. The historians will also identify the sites of lost buildings to be added.  Likewise, the church labelled as the Free Church is likely to be post-medieval, but it may be a medieval building re-used.  We’ll await conformation from the St Andrews historians that we’re working with on the project.

The road names as shown on the OS map (in this case the map is from 1914) can now be added, and the map will begin to look more like the final publication.