What is a Tithe Map?
The principal of paying a tenth of one's earnings in goods has been rooted in the Christian tradition since bibilcal times and became established in England as the country adopted Christianity in Anglo-Saxon times. The income from the tithe would support the local rector and the church building.
Over the years it became quite complicated as to who paid what to whom. Early in the 19th century it was decided to 'commute' the payments of goods into cash payments. Parliament passed the 'Commutation Act' in 1836. In quite a number of places the tithes had already been commutated but the Act meant that now all landowners had to complete the task. They were responsible for drawing up a detailed map of the lands in their tithe district. Considerable efforts were made to make the maps as accurate as possible, the best of them being 'sealed' and being treated as class one maps. Often these maps were the first accurate detailed maps of the parishes of England.
With the map complete, details on each parcel of land could then be collected and lister on the 'Apportionment' document. A number on each parcel of land links to a record in the apportionment. The system was broadly standard across the country.
The Overstrand map held in the Norfolk Record Office is a good 'second class' map. At some point this particular map ceased to be in public ownership and was discovered in the 1920s in an antique shop in Dereham.
For more detailed information on tithe maps and apportionments, you can try the following. They both have reference lists and bibliographies if you wish to study the subject further.
The Wikipedia entry for Tithe Maps is a brief, general introduction.
National Archives Research Papers has a detailed and authoritative paper on tithe maps and apportionments.