Posted on 22 August 2011 by
In creating the interactive Gough map our aim was to provide an intuitive interface to explore the map and the extensive research that aids the understanding of this valuable document..
The research team used a GIS to capture information about map features in a vector format using a high quality scan of the original map as a background. This method of data capture allows us to easily view layers of information in a GIS and our challenge was to offer as much of the same GIS functionality as possible through a web based map.
Although the Gough map conforms to no modern day geographic projection, the raster image of the map was georectified as if it were in the widely used WGS84 projection. Mapserver was used to make the image available via a Web Mapping Service (WMS). In order to make the high resolution map display quickly on demand, the images required for the WMS were pre generated and cached using Tilecache. This means that the map has been tiled into smaller images which are ready to be supplied as soon as they are requested by a browser.
The associated vector layers (such as the Rivers and Coastline layers) were also set up to be delivered via a WMS except for the Settlements layer, which was set up as Web Feature Service (WFS). The use of WFS allowed a greater flexibility in filtering and styling the features that are displayed on the map according to the search that the user performs.
The OpenLayers javascript library offers an array of functionality that was suitable for the WMS and WFS data sources that we had created and comes packaged with tools that can be customised with relative ease. Intercepting the user interactions on the map allows us to make use of the GetFeatureInfo feature of the WMS so that details can be retrieved about the points on the map that are clicked.
As the true British National Grid location had been recorded for many of the settlements identified on the map, it was possible to dynamically convert these coordinates into Latitudes and Longitudes using the Proj4 library that could be used with Google’s static map API to create a modern map image, helping contextualise the map features described in the popup boxes.