The Process of Preparing Maps

Giles Darkes, Cartographic Editor for The British Historic Towns Atlas, discusses the process of preparing the maps for the latest volume in the collection – Windsor and Eton.

When cartographers create maps, we’re always deciding what to include and what to leave out, so as to portray in as clear and honest a way the information that the reader’s looking for.  As well as simplifying a complex world and designing an attractive graphic, when you’re creating historical maps, you’ve also added dimensions to take into account: changes across time, and the uncertainty of the information.

As with any thematic map, you need to show the important information (which for us is how the towns looked at different stages of their development) against a background map.  For that background map, we sourced large-scale OS maps of Windsor and Eton dating from 1869 and 1875 (they were in different counties) and selectively digitised all the streets, buildings and their plots and other important features, including the ‘labels’ or names.  This is a time-consuming and meticulous process, but it results in a detailed, vector map which you can then use for a variety of purposes.

The most important output from this is a map showing Windsor and Eton on the cusp of industrialisation and residential expansion.  To this we’ve added the locations of the main medieval and post-medieval buildings, either showing them as they were if they survived to the 1870s or the site of them if they didn’t.  This colour map, divided into six sheets plus a sheet covering the central area, is at the heart of the atlas and gives a fantastic, summary overview of the two towns and where their main public buildings were.

Volume IV: Windsor and Eton – the latest volume from the British Historic Towns Atlas
Volume IV: Windsor and Eton – the latest volume in the British Historic Towns Atlas

But adding historical information to a map is not an easy process.  If the building survives, you can plot it on the Victorian map exactly — but of course many medieval buildings didn’t!  For certain lost buildings, archaeological information pin-points a building exactly. For others, there is good documentary evidence in the form of deeds or early maps which again can give you a pretty good idea of where a building was.  But many buildings are known about only by reference to them, or recorded on sketchy drawings, and their exact location isn’t precisely known.  For instance, on the slope of the castle leading down to Thames Street were three substantial medieval buildings: the Manor House of Underore, the Christopher Inn and one of Windsor’s bakehouses.  Remodelling of the castle and the subtle diversion of the street mean that any trace of them has long since gone, so locating them is a question of detective work and educated guesswork.

However, we’ve added them to the map.  Why? Well, the purpose of an historical atlas is to map history, and so to not put something on a map isn’t helpful!  This seems obvious, but there are pitfalls in adding information to any map.  Once you put a symbol on a map, it assumes an authority and an air of certainty that it may not merit.  Everyone has at some time used a map with a symbol which turns out to be misleading — a building shown as a pub which you find had closed down years ago when you get there, for instance!  It’s really hard for the reader to know how certain those supplying the cartographer with information are.  But to omit a building (even if its exact location isn’t known) is ultimately less helpful to the reader than putting it on the map and risking it being a little out of position.

We’ve distinguished on the map between buildings whose location and plan is known from those where we don’t know. We’ve also had to face the problem of how far you divide a large building into its different phases of construction.  We’ve distinguished between medieval (up to about 1540) and post-medieval, and in the case of a large building like Eton College, there’s good evidence of when different parts were built.  But Windsor Castle is amazingly complex and substantial parts are essentially medieval in origin but were rebuilt or re-faced in the 17th to 19th centuries.  So we have shown the whole castle as medieval, but provided in the atlas a very detailed plan of it around 1800, divided into its main phases of construction or alteration.

We’ve also used this digitised OS map to form a basis for maps showing the towns at five points in their history: 1180 to 1580 at 100-year intervals.  These are cartographic snapshots of a short period in time (about ten years either side of the date shown) with a well-researched attempt to show what was there at that time.  We’ve shown the built-up area and the principal buildings, again locating them as best we can.  It’s interesting to compare the continuity and discontinuity of settlement, and charting how the towns gradually grew but also changed shape, including losing some roads that were there in medieval times.  Look how the creation of Windsor’s Castle Park led to the closure of earlier roads, for instance.  We’ve also tried to use the names of streets or areas which are right for the time of the map.

Giles Darkes is Cartographic Editor for The British Historic Towns Atlas. Volume IV: Windsor and Eton by David Lewis is published by Oxbow Books and available to purchase now.


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