(Museum of London, United Kingdom)
Abstract: This paper will discuss the development of method to create a geo-referenced index of mid-eighteenth streets and places in London to spatially enable researcher’s data, , and an authoritative geo-referenced version of a prime contemporary map. These resources will be made available
The processing involves the creation of a connected network of streets, accompanied by a polygon layer of open areas and discrete buildings (parks, squares etc) from the first reliable mapping we have for the area, (c.1850). These datasets are then manipulated using GIS models to create a layer of connected, correctly abutted and clipped polygons. Geographic transformations are then performed on an existing street/place index of 1746 points, to convert their solely graphical pixel-based coordinates to those on the British National grid. This allows them to be plotted over the clipped polygon layer and thereby gives those polygons their identity. The polygons are then iteratively clipped by the larger order polygon data sets created for the area; parishes, wards and counties, so as to derive a polygons segment for each combination.
By groundling the method in the first truly reliable mapping available for the area, rather than the project’s target mapping (1746) we have a sound basis for the incorporation of other historic cartographic resources. The process of creating street networks and polygon layers and their indexing for earlier or later maps of the area becomes one of editing, and extension/clipping rather than starting from scratch. Various issues will be discussed such as the optimum digitization method given that some areas will have changed, the utility of connected network routing in the historic context and the need to concentrate on the geographically rather than pictorially accurate presentation of data.
Keywords: georeferencing, historic maps, gis-models