You may have seen that The Genealogist recently digitised further tithe maps and apportionments for Middlesex, Surrey, Buckinghamshire and Leicestershire in partnership with the National Archives.
If you're interested in Norfolk's maps, then you'll love www.historic-maps.norfolk.gov.uk where you can view most of the County tithe maps in colour for free from any computer with an internet connection. You'll also find you can view a modern map, 1988 and 1946 aerial photographs, the first edition OS map at six-inch to the mile scale (c1885) and even some enclosure maps (late 1700s/early 1800s). There are also some additional maps of Norwich, Great Yarmouth and King's Lynn, as well as Bryant's and Faden's maps (some of which are also available elsewhere - for example the redrawn Faden's map by Andrew Mcnair).
Historic Maps lets you switch on and off the different layers in the Map Explorer, drag around the screen, and even split the screen to view two maps of the same area side by side. For someone with a minor map addiction, this is one of my favourite websites!
Now, where it comes to the Norfolk apportionments, for the time being you'll need to visit Norfolk Record Office (at the Archive Centre) or Norfolk Heritage Centre (inside the Millennium Library). These records make the maps themselves a great deal more useful, as they match each numbered plot to the owner, occupier and use of the land. I'd suggest taking a laptop to use the map and apportionment side by side, or bagging two microfilm readers next to each other to look at two films simultaneously (keep in mind though that tithe maps on film are black and white where the digital versions are in colour). Unlike most records, you can put a specific person in a specific building.
The timing of the tithe maps (mostly 1836-41), makes them very useful to compare to the 1841 census, land tax records, early electoral registers and manorial records.
One word of warning - not every parish had a tithe map, but most do, although they are of varying quality and accuracy. Where tithes were already commuted by the time of the Act in 1836, a map was not necessary. Don't be put off if you're looking at a now very urban area: even some Norwich parishes have them as in 1836 the area was not as built up.
Where one was created, there may be as many as three copies in existence. There is usually one at The National Archives in the Tithe Commissioners' archives, and one or two further copies held locally because parish and diocese were originally provided with one each - both of these originals could now be with the local Diocesan archive where surviving. For almost all parishes in Norfolk the Diocesan record office is Norfolk Record Office.
A tip to find tithe maps on the NRO catalogue - type 'DN/TA' into the CatRef field on the advanced search and the name of the parish in Any Words. This means that you only search Tithe records in the Diocese of Norwich. Try with Wymondham, for example, and you'll find the tithe map and apportionment under the reference DN/TA 448. The map is dated 1839 and the first apportionment 1841. For parishes in the Ely Diocese, use DE/TA instead.