The images were created from the LDS microfilm copies of the originals. This means that the sequence of images online follows the sequence on the microfilm, which in turn follows the arrangement of the originals: the returns for each townland or street are grouped together and preceded by Form N, Form B1 and, if one exists, Form B2. There is no facility on the site to browse through the returns sequentially, as they appear on the microfilm, but it is possible to do this simply by adding or subtracting 1 from the file number (starting 'nai' ) in your browser's address bar. This can be useful if you suspect that a household return has been omitted from the transcription. At the time of writing, a significant number of returns, particularly related to single-street villages, remain untranscribed, but it is possible to track down the images.
One further consequence of the use of the microfilm copies is worth keeping in mind: the microfilm of 1901 omitted the reverse of the majority of returns. This is where specific place-identifying information was recorded-street numbers, townlands, parishes-and its omission is regrettable. However, almost all the information can be reconstructed from the enumerator's abstract (Form N). Unlike most if not all the overseas census material now searchable online, the Irish 1901 and 1911 returns are the originals filled out by the householders themselves and have a vivid immediacy that can be very poignant.
District Electoral Divisions originated as subdivisions of a Poor Law Union, grouping together a number of townlands to create a constituency for the election of members to a Poor Law Board of Guardians. As the Poor Law was funded by property taxes, the aim in creating the DEDs was to have areas that produced roughly similar tax takes. This meant that their boundaries ignored natural community borders, such as counties or parishes. It also means that it can be difficult to work out the geographical relationship between DEDs. The only readily accessible map of DEDs dates from the 1930s and can be found on the website of the Irish Placenames Commission, www.logainm.ie, in 'Information resources'/'The Placenames Branch', under "Historical maps > Boundaries".
In urban areas the problems posed by DEDs are even more acute. A boundary could run down the middle of a street or bisect it in other ways, with a slightly different spelling in the other DED. The only way to reconstruct all the returns for a particular street is to use great care and many wild-card searches in the Townland/Street field.
The most straightforward, though cumbersome, way to cover a large area is to
take all the townlands in a particular civil parish and check their deds in the 1901
Townlands Index. The 1841 Townlands Index, also known as Addenda to the 1841
Census, available on request from the nai reading room staff or in the National
Library (Ir 310 c 1), organises townlands alphabetically within civil parishes.