landscape & local history research group

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Bulletin 8: Sources and Research Methods: Some New Approaches

June 2021

Contents

Geographical Information Systems for Historians 1  William Franklin

The Archive at Your Desk: Researching local and urban landscapes using digital sources Denise McHugh

‘You can prove anything with statistics’ Ken Sneath

All articles are © the Authors, 2021.

Published by the Cambridgeshire Association for Local History

Geographical Information Systems for Historians

William Franklin

Summary

Traditionally, historians have relied on the human eye to interpret old maps and the human hand to produce maps that display complex data in a meaningful way for readers. The latter can take many hours, and for every permutation of data to be displayed, a new map hand drawn. The advent of free-to-use Graphical Information Systems (GIS) now give historians new opportunities both in the interpretation of data and its display. This article, based upon my own use, considers the use of GIS in the study of landscapes.

Maps

While data from many types of documents can be used spatially, it is in the study of the historic landscape through maps that Geographical Information Systems are a particularly useful tool. I make no apology for highlighting this particular use above others in this paper.

There are a variety of types of map that can be used for such study: county, estate, enclosure and tithe, as well as maps made for specific uses, such as the route of railways and turnpike roads or for travelling from place to place. All have advantages and limitations of use. What they depict, how it is shown and, equally importantly, what they omit, depends on the type of map and its purpose. Some maps are linked to a specific process, such as enclosure or tithe commutation, while those grouped under the umbrella of estate maps might have been commissioned for a variety of reasons. These issues and more are discussed in detail in Catherine Delano-Smith and Roger Kain’s English Maps, while Sarah Bendall provides a thorough examination of the estate map.1 It is not the intention to repeat general principles already established by these scholars or to give a history of map making here.

Care must be taken when extracting information from maps as, regardless of how detailed or finely drawn they might be, all maps require interpretation. When originals are unobtainable, copies must be used. Copies need to be treated with caution: negative images will have lost any information contained within colouration and shading; estate copies of enclosure or tithe maps might omit information not relevant to that particular estate; estate copies of earlier maps, even from the same estate, might include changes made in the period since the making of the original but this may not be indicated on the map.2 All maps are somewhat cavalier in their treatment of features beyond the remit of that particular map. For example, a c1812 map of Eltisley possibly produced for an early attempt at enclosure does not show a large, moated area next to the church, now known to exist at that time, and shows another large moat at right angles to its actual position.3 Here the map maker was interested in the fields and furlongs of the parish and not other aspects of the historic landscape such as moats.

The condition of a map can also affect its usefulness. Those held in modern archives are stored in climate-controlled atmospheres and are carefully protected and repaired. But some have evidence of neglect and damage prior to their deposition; they might be dirty, torn, water and mould damaged, or written upon, and for some the damage is irreparable, leading to a serious loss of information. Many suffer from simply being old and faded, while those behind glass are extremely difficult to photograph and it is good quality, high resolution photographs of maps that we want when working with Geographical Information Systems. As we shall see later, we do not necessarily require a whole map to be photographed as one image, but we do require the whole map in as many images as it takes.

Traditionally, local and landscape historians will have viewed every detail of a map taking notes and sometimes laboriously made a tracing. With the advent of photography, photographs could be made of all or part of a map, which alongside notes, (particularly important if the photographs were black and white), were then studied in detail. However, the issue remained about how to place features in the modern landscape especially if that landscape had significantly changed. The historian using a geographical information system will still encounter this difficulty, but to a lesser degree.

Aerial Photographs

Like maps, aerial photographs provide a snapshot of an area of landscape at a particular moment in time. Those taken by Cambridge University, the Royal Airforce and the Luftwaffe may be particularly useful as they pre-date the shift to prairie style farming and more recent large scale housing developments. From such photographs we can trace certain ephemeral features such as field patterns, pastures, parks, and woods.

Geographical Information Systems

Having considered our primary sources, let us now consider the tools: the Geographical Information System (GIS). GIS have been around since the late 1960s and started to become popular tools in the 1990s when they were used by commercial mapping companies, institutions, and government departments such as local public health departments. GIS is computer-based software and as computing has developed, so has the software. As recently as fifteen years ago GIS software was very expensive and well beyond the pocket of most historians. A collaboration of programmers from around the world interested in GIS changed all that. In about 2005 they produced some basic but free software called Quantum GIS (now known as QGIS), which has developed over the last fifteen years into a program that is a match for any commercial system and remains free.4 As free software, it is available for the use of historians and archaeologists to use.

But what is a Geographical Information System? Quite simply, it is a specialised form of database in which the data in the form of shapes, known as points, lines and polygons are usually, although as we shall see not always, drawn on screen and on to a map. Like any traditional database, the attribute data is stored in rows and columns, and provides a structure in which the features in the database can be queried and analysed regarding what and where they are.

GIS and Historical Research

The integration of the disciplines of history and geography has developed since the 1950s in order to incorporate both spatial and temporal elements of history, thus allowing for further research and analysis than might otherwise be possible in a short period of time and providing both historians and geographers with a visual means of analysing complicated information.

Local and landscape historians recognise that all human interaction with others and the environment has inherent spatial characteristics, although not always explicitly addressed in the research. Siebert, studying the spatial history of Tokyo, noted the importance of the geographical component of historical studies:

There is a simple, two-part answer. First, humans are spatial beings. Individuals, groups, and institutions exist and interact in natural human environments that occupy space over time. Human history necessarily includes a spatial dimension, which historians often overlook. Second, geographic information systems are designed to record spatial features and related information, display them, and analyse their conditions and spatial relationships. These capacities enable spatial historical research and extend its analytical reach. 5

GIS therefore offers numerous possibilities for expanding our knowledge and examining more widely some of the issues that intertest us, whether that be at a local level in mapping social status, tenure, and income etc. in a town or village, or mapping taxation data at a district or county level, studying the effects of enclosure or a whole range of other topics.

Things to know about using a Geographical Information System

GIS software is nothing but a blank screen without base maps. The Ordnance Survey makes available a range of free digital maps that can be used in conjunction with most GIS (including QGIS) as a base map.6 In addition, Google Earth (basic maps, terrain maps and Satellite imagery) as well as a range of other regularly used computer mapping services can all be used in QGIS. A word of caution, free maps from the Ordnance Survey use the British National Grid (BNG) as their coordinate system, whereas most free computer mapping systems such as Google Maps use a system known as Pseudo-Mercator. The two projections are different, and the same feature is often many metres apart.7 I do not intend to discuss the differences in coordinate referencing systems here as that would require a very long article. What can be said here is that GIS can add a large range of free maps and satellite applications within them, and if you have bespoke maps or images created in, for example, Google Earth and then exported as a Keyhole Markup Language (.kml) file, these can be easily imported.

A geographical information system, like any project or database, requires a bit of planning, both in terms of what data you want to capture and where you store your data. Every layer and photo should be kept in a specific location, so that when you open the GIS it loads the associated files. Not doing so will cause the program to stop loading until you have relinked each item at start-up, which could prove tedious if you have a lot of layers on your map.

Broadly, GIS software packages handle two types of file: Raster, and Vector. Any paper map you photograph and load into a GIS will be a Raster file. Its properties are fixed, whereas points, lines and polygons as digitally drawn features are Vector files and can be manipulated in many ways. A modern digital map is built up of a series of vectors displayed at the same time, for example, a river will have its banks outlined by lines which are held in one file, whereas the coloured infill of the river will be a polygon and stored in another file. If we are building up a map using historic data it is vector data we are primarily concerned with, because each vector file will contain a table of data behind it, whereas we cannot assign data to a raster file.

Entering data into a GIS is time consuming. With a database, data is entered and analysed relatively quickly (assuming you have reasonable typing skills), but then producing your data manually in ways that visually tell the story or highlight the points you wish to make can be very time consuming. Using a GIS means drawing the features and populating the database at the same time. That is time consuming, whereas analysing the data and producing a wide range of visual data is relatively easy.

Before considering how we might use a GIS there are some things that need to be defined. I have already said that vectors such as points, lines and polygons are the visual aspects of a data table, points allow the user to assign a precise location to something. A point is a dot or other symbol displayed at the vertex at which the lines of longitude (x) and latitude (y) intersect. The user can assign a value to a point, such as a feature (a well, spring, tree etc.), or a place (hamlet, village, town, or city), etc. Lines, sometimes called polylines, can be drawn to outline features or show the presence of something linear, such as a road or hedges. Polygons are a series of connected lines that represent an area such as the outline of a building, the extent of a town or the area of a county.

GIS and historic maps

You are probably by now thinking: “how on earth do I get the historic map I photographed into my GIS?”. The simple answer is by digitising it. Within its tools, QGIS (along with most other GIS packages) contains a tool called a georeferencer. In QGIS, when this is selected a second window pops onto the computer screen into which you load a digital photograph of a map. You then must look at your photograph and the modern map side-by-side and identify features common to both. Let us say your picture contains a churchyard and surrounding streets. You select the corners of the churchyard, one at a time, by putting a marker on a point in the photograph and on the corresponding place on the modern map. When done, the program overlays the photograph of the old map on to the modern map.

Once overlaid, it is possible to make the photograph transparent so that you can see the differences between the two maps. If you photographed a very large map in sections, you might have to repeat the process for every picture. It is therefore best, whenever possible, to have one photograph of the whole map you are digitising. But please, make sure you can read every bit of text, because if you cannot, your assigning data to each feature as you digitally trace it will be much slower as you constantly need to refer to more detailed photographs of part of the map or notes you have taken.

Figure 1. (left) The Green at Wicken overlaid onto the modern (colour) digital Openstreet Map