As to the use (or not) of Google: one of the priorities for the map here was that it preserved the individual layers of GIS data in a way that allowed users to turn them on and off. So, there is not a single overlay, but anywhere up to 26, and this is one of the things contributing to the loading time of the map. Although it is definitely possible to convert GIS shapefiles into the KML format used by Google Maps, it is a fair bit of work to get the map projection correct, and to build a viewing environment that will display them in the way we wanted here. In due course we will be adding the shapefile attribute data to the High Bandwidth map, and this would again be less easy to do if were using Google Maps.

One additional consideration is that the maps you see here are served entirely from our own servers, and so we don’t need to worry about the Google Map API changing in the future – the maps here will remain visible come what may. Finally there is no way to build a low-bandwidth / no JavaScript map with Google Maps (which we provide here as the ‘Low Bandwidth’ map).

Having said all the above, we are looking into building an additional map which will allow overlay of the layers we have created with Google Maps data, primarily to give a better sense of medieval Chester in the context of modern Chester.