Tong Maps
Use the button to select the date of the historical map to use as an overlay and then use the slider at top right to change the transparency of the current historical map layer, so you can compare it with the current Google map of Tong.
Map for 1765 Map for 1901 Map for 2007
The javascript code for the opacity slider is based on Gavin Harriss' which was originally developed for: New Zealand Topography map