Perhaps we never dreamed to see one day a historical map, mounted on Google, such that we could know how 300 was years ago the land where we stand today.
Web mapping technology has allowed this. And wow! how.
An example of this is the nostalgic map of London, where not only have they published an 1746 cartography, but they have also informed the methodology they have followed to adjust it to cadastral maps of more than two decades.
It is definitely an exemplary work, in which period maps between 1869 and 1890 that were probably paper have been used, which have been carefully scanned to maintain the level of detail that was an art in those days.
As a result, it is likely to do things like this. Surprising how where the urban nucleus is now some day were clearly defined farms in old-fashioned cartography.
To integrate this work, after the scan, they had to do a coupling job where the frequent individual errors in each sheet, in overlap are almost impossible to detect. Not an easy thing to do, since time causes the sheets to deform, added to what happens when the work goes through a scanner.
Then they have collected hundreds of known points in the field, separated by each of the maps.
Working a large amount of maps of a wide area, raised with old methods, generates problems of rotation, georeference, such that stretching one side causes another to be disarmed, even within the same sheet.
For this, they have done the identification of streets axes, to complete a network topology with which to make a stretch to the image of differentiated form.
Thus, using a forensic method, when stretching, the map has been accommodated as close as possible as if it were an ortho-referenced map.
An interesting problem is all the areas that have been transformed, such as train areas, where it is impossible to determine known points. For this they have resorted to a somewhat difficult method to fully understand, generating buffers from the street axes, taking into account the gauges used at that time. And with this they have achieved an even more accurate transformation.
In conclusion, a great example of what can be done using the technical and technological capabilities available. And a great sorrow for those who have sent to the cellar of a bath those maps that were raised with empirical methods, but whose historical value we are not able to appreciate ... for now.